Systemic targeted anti-cancer therapies selectively target cancerous cells whilst limiting systemic side effects. The eye however, is a particularly sensitive organ and the expanding use of the newer targeted chemotherapy agents has been associated with multiple ocular side effects. In this review we provide an update of the ocular side effects of the newer targeted chemotherapy agents along with suggested minimum, pragmatic, evidence-based strategies for effective screening or monitoring for potential ocular side effects. This framework is designed to guide oncologists, trial managers, protocol developers and regulatory authorities so that appropriate ophthalmic clinical examinations and non-invasive modern imaging can be requested and commissioned according to a patient's specific treatment.

The advent of next-generation antibody-drug conjugates (ADCs), particularly trastuzumab deruxtecan (T-DXd), has transformed our understanding of human epidermal growth factor receptor 2 (HER2) targetability for breast cancer (BC) treatment. Historically categorized as HER2-positive or HER2-negative on the basis of trastuzumab eligibility, this classification has evolved significantly over the past 5 years. The DESTINY-Breast04 trial marked the entry of anti-HER2 therapies for patients with HER2-low BC, while DESTINY-Breast06 demonstrated the potential for earlier and broader use of T-DXd. The latter trial revealed that even minimal HER2 expression in tumors previously classified as HER2-0 might be clinically relevant and targetable with T-DXd. This has led to further refinement of HER2 classification, introducing the concepts of HER2-ultralow (HER2-0 with staining) and HER2-null BC (HER2-0 without staining). With these findings, most patients with metastatic BC are currently considered eligible for T-DXd. Accurately identifying candidates for these therapies has highlighted the limitations of current HER2 diagnostic practices, on the basis of immunohistochemistry (IHC)/in situ hybridization assessment. IHC assay, optimized to detect high levels of HER2 protein, faces limitations in discriminating finer variations at the lower end of the HER2 expression spectrum. This is further complicated by the heterogeneity of HER2 expression. To overcome these barriers, new approaches may be required. Quantitative methods for HER2 membrane assessment, genomic and transcriptomic evaluations of HER2, and the integration of artificial intelligence into tissue analysis hold promise and are currently under investigation. Additionally, noninvasive strategies, such as analysis of circulating tumor DNA or circulating tumor cells, may enable real-time HER2 status assessment and better patient selection for ADC. However, these techniques require rigorous validation to ensure their clinical utility. This evolving landscape underscores the need for improvement of diagnostic approaches to support the expanding role of ADCs in BC treatment.

Trastuzumab deruxtecan (T-DXd), a human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate, demonstrated remarkable efficacy in previously treated patients with HER2-low metastatic breast cancer (mBC), marking a new therapeutic option for this patient population. Prior studies with HER2 PET using 89Zr-radiolabeled antibodies were limited by high rates of imaging false positives for HER2-positive malignancy. In this retrospective study, we investigate whether these false positives (HER2-negative on pathology) could be explained by HER2-low lesions. Methods: A retrospective study was conducted of mBC patients who previously enrolled in 2 prospective HER2 PET imaging trials: NCT02286843 using 89Zr-trastuzumab and 89Zr-pertuzumab and NCT04692831 using 89Zr-ss-pertuzumab. Patients were included if paired HER2 PET scan and biopsy were performed within a 2-mo period. Of 56 total patients, 23 patients met the inclusion criteria. Pathology results for biopsied lesions were collected, without repeat interpretation, and lesions were classified as HER2-positive, HER2-low, or HER2-0. SUVmax of biopsied lesions were compared between pathologic classifications to determine whether lesion uptake intensity could differentiate between HER2-positive and HER2-low lesions. Results: All prior false-positive lesions on HER2 PET scans from NCT02286843 were reclassified as HER2-low (instead of HER2-negative). In the 89Zr-trastuzumab cohort, 3 lesions were HER2-positive (33%) and 6 were HER2-low (67%); in the 89Zr-pertuzumab cohort, 2 were HER2-positive (29%) and 5 were HER2-low (71%). In the 89Zr-ss-pertuzumab cohort (NCT04692831), 7 patients underwent recent biopsies of 8 total lesions demonstrating 1 HER2-positive (12%), 5 HER2-low (62%), and 2 HER2-0 lesions (25%). HER2 PET SUVmax of biopsied lesions were compared between HER2-positive and HER2-low lesions for the combination of all 3 radiotracer cohorts. HER2-low lesions had a significantly higher SUVmax (median, 12.7; interquartile range, 8.05) than did HER2-positive lesions (median, 6.4; interquartile range, 1.98; P = 0.01). Conclusion: HER2 PET imaging with 89Zr-radiolabeled antibodies detects HER2-low lesions in addition to HER2-positive lesions in patients with mBC, suggesting its ability to visualize the entire spectrum of HER2 expression. All prior false positives on 89Zr-trastuzumab and 89Zr-pertuzumab PET scans were reclassified as HER2-low. Lesion SUVmax is not reliable in differentiating HER2-positive from HER2-low lesions; however, it may be useful in distinguishing lesions expressing HER2 from HER2-0 lesions.

A 25-year-old man presented with a locally advanced lacrimal gland adenocarcinoma with parotid metastasis. The lesion was strongly HER-2 positive (3+) on immunohistochemistry. The patient was treated with neoadjuvant trastuzumab emtansine, an antibody-drug conjugate targeting HER-2. The patient had an excellent response to neoadjuvant therapy trastuzumab emtansine, with a significant decrease in the size of the lacrimal gland carcinoma, making eye-sparing surgery a viable option for the patient. Furthermore, there was nearly complete resolution of the parotid metastasis; thus, radical neck dissection and parotidectomy were avoided.

Antibody-drug conjugates (ADCs) are a rapidly evolving class of antitumor drugs and have already revolutionized the treatment strategy of many hematologic and solid cancers. So far, trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd), sacituzumab govitecan (SG) and datopotamab deruxtecan (Dato-DXd) are the four ADCs that have been approved by US food and drug administration (FDA) in treatment of breast cancer, and SKB264 has been approved by Chinese national medical products administration (NMPA). Many ADCs for treatment of breast cancer are currently being tested in late-phase clinical trials, with several encouraging results achieved recently. However, major issues arise during the use of ADCs, including emergence of acquired resistance, occurrence of treated-related toxicities, and identification of biomarkers of response and resistance. ADCs are being increasingly tested in combination with other agents, and novel next-generation ADC development is progressing rapidly. A better understanding of the design and development of ADCs will promote ADC development for cancer treatment. In this review, we aim to provide a broad overview of the design and the recent advances of ADCs in breast cancer. We also propose several notable future directions of ADCs in treatment of breast cancer.

Human epidermal growth factor receptor 2 (HER2)-low breast cancer is defined as breast cancer with an immunohistochemistry (IHC) score of 1+ or 2+ and in situ hybridisation (ISH)-negative. The traditional HER2 classification (negative or positive) has limitations, with only 15%-20% of the breast cancer population being positive and suitable for HER2-targeted therapy. The new clinical study, DESTINY-Breast04, shows that trastuzumab deruxtecan (T-DXd) has a significant effect on advanced HER2-low breast cancers, a classification that accounts for approximately half of the advanced breast cancer population. However, the detection methods and evaluation criteria for HER2-low breast cancer have not yet been standardised, and the toxicity and resistance mechanisms associated with T-DXd therapy are still unclear. This article focuses on these issues and describes the progress and challenges of T-DXd-related therapy in the treatment of advanced breast cancer patients with low HER2 expression.

Antibody-drug conjugates are novel antineoplastic agents whose use is expanding, both in terms of the number of drugs and the number of patients being treated. This article reviews the known toxicities and complications of antibody-drug conjugates that are currently approved for the treatment of cancer in the United States, with a focus on their emergency presentation and management. Similar to many other cancer therapies, most antibody-drug conjugates can cause diarrhea, nausea/vomiting, rash, peripheral neuropathy, and cytopenia, which are generally treated following standard-of-care. Interstitial lung disease, which may mimic pneumonia and cause respiratory failure and death, has been seen with trastuzumab deruxtecan and mirvetuximab soravtansine; emergency treatment of this condition includes oxygenation, ventilatory support, and corticosteroids. Inotuzumab ozogamicin and gemtuzumab ozogamicin are both associated with sinusoidal obstruction syndrome, a potentially fatal liver dysfunction that presents with weight gain, fluid overload, and jaundice. Abnormal liver function tests in patients who have been recently treated with these agents should be cautiously evaluated. Cardiac adverse events with antibody-drug conjugates are rare, but trastuzumab emtansine and trastuzumab deruxtecan may cause a decrease in cardiac contractility, and heart rate corrected QT interval prolongation is a rare effect of trastuzumab deruxtecan. Ocular adverse events, especially blurred vision, and keratopathy, are common with mirvetuximab soravtansine and tisotumab vedotin. Progressive multifocal leukoencephalopathy has been reported with brentuximab vedotin and polatuzumab vedotin. Tumor lysis syndrome may occur after treatment with gemtuzumab ozogamicin, polatuzumab vedotin, and brentuximab vedotin. Patients receiving enfortumab vedotin or brentuximab vedotin may develop hyperglycemia, sometimes presenting as diabetic ketoacidosis. Tisotumab vedotin and trastuzumab emtansine are associated with bleeding; although it is minor in most cases, severe bleeding and intracranial hemorrhage have occurred. Several antibody-drug conjugates can cause an anaphylactoid infusion-related reaction, which occurs most commonly during or soon after infusion but may be delayed up to 24 hours. Further research is needed to establish the real-world incidence of rare complications and how often patients with these complications present to the emergency department.

Human epidermal growth factor receptor 2 (HER2) is one of the oncogenic drivers of breast cancer and is often used as a definitive therapeutic marker for breast cancer. This has led to significant improvements in both targeted therapy and prognosis for HER2-targeted breast cancer. Due to the differences in HER2 gene and protein expression levels, they are clinically classified into HER2 zero-expression breast cancer, low-expression breast cancer and high-expression breast cancer. Among them, HER2 low-expression is considered a special expression state, which is insensitive to conventional anti-HER2 therapy and has a poorer prognosis and thus has received attention from researchers. Some studies demonstrate that patients with HER2 low-expression can benefit from antibody-drug conjugates (ADC). Several studies are currently exploring the efficacy of various ADC drugs in breast cancer with HER2 low-expression, opening up new treatment avenues for patients with HER2 low-expression breast cancer. This review aims to summarize the clinical features of HER2 low-expression breast cancer and the recent advances in its therapeutic agents.

Antibodies have gained clinical success in the last two decades for the targeted delivery of highly toxic small molecule chemotherapeutics. Yet antibody-drug conjugates (ADCs) often fail in the clinic due to the development of resistance. The delivery of two mechanistically distinct small molecule drugs on one antibody is of increasing interest to overcome these challenges with single-drug ADCs. We have developed a modular synthetic strategy for the construction of a library of 19 dual-drug ADCs where drugs are conjugated through unnatural cyclopentadiene-containing amino acids and native cysteine residues on an anti-HER2 trastuzumab scaffold. Importantly, this strategy utilizes the same functional group on the linker-drug construct; this allows for the facile addition of drugs at either conjugation site and enables the evaluation of different drug-to-antibody ratios and combinations of drug pairs. We tested the library on high- and mid-HER2 expressing cell lines and observed increased toxicity in several dual-drug ADCs compared with single-drug constructs. The strategy developed herein provides a method for the facile synthesis, characterization, and evaluation of dual-payload ADCs. Simultaneous delivery of combinations of drugs with distinct mechanisms of action is critical for the next generation of targeted drug delivery.

The advent of immune checkpoint inhibitors (ICIs) has deeply reshaped the therapeutic algorithm of triple-negative breast cancer (TNBC). However, there is considerable scope for better engagement of the immune system in other BC subtypes. ICIs have paved the way for investigations into emerging immunotherapeutic strategies, such as immune cell engagers (ICEs) that work by promoting efficient tumor cell killing through the redirection of immune system against cancer cells. Most ICEs are bispecific antibodies that simultaneously recognize and bind to both cancer and immune cells generating an artificial synapse. Major side effects are cytokine release syndrome, hepatotoxicity, and neurotoxicity related to inappropriate immune system activation. Here, we provide a comprehensive overview of this compounds, the available preclinical and clinical evidence supporting their investigation and development in BC also highlighting the challenges that have prevented their widespread use in oncology. Finally, major strategies are explored to broaden their use in BC.

Antibody-drug conjugates (ADCs) are antitumor drugs composed of monoclonal antibodies and cytotoxic payload covalently coupled by a linker. Currently, 15 ADCs have been clinically approved worldwide. More than 100 clinical trials at different phases are underway to investigate the newly developed ADCs. ADCs represent one of the fastest growing classes of targeted antitumor drugs in oncology drug development. It takes advantage of the specific targeting of tumor-specific antigen by antibodies to deliver cytotoxic chemotherapeutic drugs precisely to tumor cells, thereby producing promising antitumor efficacy and favorable adverse effect profiles. However, emergence of drug resistance has severely hindered the clinical efficacy of ADCs. In this review, we introduce the structure and mechanism of ADCs, describe the development of ADCs, summarized the latest research about the mechanisms of ADC resistance, discussed the strategies to overcome ADCs resistance, and predicted biomarkers for treatment response to ADC, aiming to contribute to the development of ADCs in the future.

Non-small cell lung cancer (NSCLC) has a strikingly high incidence rate globally. Although immunotherapy brings a great breakthrough in its clinical treatment of NSCLC, significant challenges still need to be overcome. The development of novel multi-functional nanomedicines in the realm of tumor immunotherapy offers promising opportunities for NSCLC patients, as nanomedicines exhibit significant advantages, including specific targeting of tumor cells, improved drug bioavailability, reduced systemic toxicity, and overcoming of immune resistance. In this review, the core features and current clinical status of strategies for NSCLC immunotherapy including immune checkpoint blockade, antibody-drug conjugates, cell engagers, adoptive cells, and cancer vaccines, are surveyed. Particular emphasis is placed on the recent development of nanomedicines that boost these strategies. Nanomedicine can provide novel perspectives for NSCLC immunotherapy.

Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate of trastuzumab and the cytotoxic agent emtansine (DM1), approved for use as an adjuvant treatment for patients with residual disease after neoadjuvant chemotherapy and antihuman epidermal growth factor receptor 2 (HER-2) therapy and in metastatic HER-2-positive breast cancer. Previous studies have shown that T-DM1 has a favorable safety profile, with few high-grade toxicities reported so far. We describe a patient who developed profound hyponatremia-which has not been reported previously-following treatment with adjuvant T-DM1 for HER-2+ breast cancer.

Trastuzumab improved the prognosis of patients with human epidermal growth factor receptor 2 (HER2)+ breast cancer (BC). Here, we present a patient who developed acute vision loss due to optic atrophy in both eyes after trastuzumab.

A 60-year-old female patient was diagnosed with locally advanced HER2+ BC in January 2021. After four cycles of neoadjuvant anthracycline-based chemotherapy followed by four cycles of docetaxel, trastuzumab, and pertuzumab combined treatment, the patient underwent a right modified radical mastectomy. Three days after the end of the second cycle of adjuvant trastuzumab, she presented with acute vision loss. The patient's visual acuity was 90% in the right eye and 60% in the left eye. The left eye had optic nerve edema and spindle hemorrhages. First, on suspicion of optic neuritis, the patient was given a 1 gram/day pulse steroid for three days. However, optic neuritis was not considered during the follow-up. Metastasis was considered at the exit of the left optic nerve. Trastuzumab was started by making a mutual decision with the patient. Six days after the sixth dose of adjuvant trastuzumab, she presented with almost complete vision loss.

The patient was diagnosed with optic neuritis, and a pulse steroid was administered. Trastuzumab was permanently discontinued. However, the patient's visual acuity in both eyes remained at 5-10%.

Vision loss due to optic neuritis is a devastating side effect. Understanding that trastuzumab-induced optic neuritis may develop will help clinicians detect side effects early and manage them more effectively.

While in theory antibody drug conjugates (ADCs) deliver high-dose chemotherapy directly to target cells, numerous side effects are observed in clinical practice. We sought to determine the effect of linker design (cleavable versus non-cleavable), drug-to-antibody ratio (DAR), and free payload concentration on systemic toxicity. Two systematic reviews were performed via PubMed search of clinical trials published between January 1998-July 2022. Eligible studies: (1) clinical trial for cancer therapy in adults, (2) ≥ 1 study arm included a single-agent ADC, (3) ADC used was commercially available/FDA-approved. Data was extracted and pooled using generalized linear mixed effects logistic models. 40 clinical trials involving 7,879 patients from 11 ADCs, including 9 ADCs with cleavable linkers (N = 2,985) and 2 with non-cleavable linkers (N = 4,894), were included. Significantly more composite adverse events (AEs) ≥ grade 3 occurred in patients in the cleavable linkers arm (47%) compared with the non-cleavable arm (34%). When adjusted for DAR, for grade ≥ 3 toxicities, non-cleavable linkers remained independently associated with lower toxicity for any AE (p = 0.002). Higher DAR was significantly associated with higher probability of grade ≥ 3 toxicity for any AE. There was also a significant interaction between cleavability status and DAR for any AE (p = 0.002). Finally, higher measured systemic free payload concentrations were significantly associated with higher DARs (p = 0.043). Our results support the hypothesis that ADCs with cleavable linkers result in premature payload release, leading to increased systemic free payload concentrations and associated toxicities. This may help to inform future ADC design and rational clinical application.

Antibody-drug conjugates (ADCs) are increasingly utilized in patients with solid tumors and hematologic malignancies. However, the adverse ocular toxicity induced by ADCs has not been comprehensively evaluated in real-world clinical settings.

Data from April 2019 to March 2024 based on the FDA Adverse Event Reporting System (FAERS) were extracted and analyzed. Disproportionality analysis was used to evaluate the association between ADCs and ocular adverse events (AEs). The median time to onset (TTO) of various ADCs was compared.

A comprehensive analysis identified 2,686 ocular AEs associated with ADCs. Among these, Tisotumab vedotin had the most positive signals at the preferred terms (PTs) level, followed by trastuzumab emtansine and enfortumab vedotin. In contrast, gemtuzumab ozogamicin demonstrated minimal ocular toxicity signals. Cluster analysis revealed that ADC-related ocular toxicities predominantly manifested as corneal disorders or ocular neuromuscular disorders. The median onset of ocular toxicity varied considerably, with enfortumab vedotin showing the earliest median onset at 12.5 days.

Our study demonstrates the association between ADCs and ocular AEs based on real-world data, providing valuable guidance for clinicians when prescribing ADCs. And we found some important safety signals that have not been mentioned in the label or previous studies.

To evaluate the prevalence and characteristics of different HER2 categories among patients with advanced breast cancer (aBC) and describe treatment patterns and outcomes of those with HER2-low disease.

A retrospective cohort study was conducted via chart review at the Huntsman Cancer Institute, including patients diagnosed with aBC (stages IIIB, IIIC and IV) between 2010 and 2019. All patients with IHC1+ were considered HER2-low unless FISH was positive. Patients with IHC2+ were only classified as HER2-low if a negative FISH was documented. The prevalence and characteristics of each HER2 category were reported. Treatment patterns and survival outcomes of HER2-low patients who received first line treatment in 2017 or later were presented.

A total of 240 of 414 patients (58%) with aBC were HER2-low, with the majority of patients (83%) classified as hormone receptor (HR)-positive. In first line, most HR-positive patients received endocrine therapy with chemotherapy for stage IIIB/IIIC (47%) and with CDK4/6 inhibitors for stage IV breast cancer (50%) Most HR-negative patients received chemotherapy alone (92% for stage IIIB/IIIC, 60% for stage IV). In second line, chemotherapy alone was the most common modality (21.4% for HR-positive; 45.5% for HR-negative). Median overall survival was 37.7 months while median progression-free survival from first line was 18.0 months, decreasing to 8.0 months in second line.

A substantial proportion of patients previously classified as HER2-negative have low but detectable HER2 expression and may benefit from novel HER2-directed agents, which have demonstrated clinical benefit in this population post-chemotherapy.

With the approval of trastuzumab deruxtecan for the treatment of unresectable/metastatic HER2-low breast cancer, human epidermal growth factor receptor 2 (HER2)-low has emerged as a clinically actionable biomarker. There is an urgent need for a deeper understanding of HER2-low breast cancer patients. Therefore, this study was conducted to explore the clinicopathological characteristics, the evolution of HER2-low status, and its impact on the prognosis of hormone receptor (HoR)-negative/HER2-low metastatic breast cancer (MBC) patients.

This pooled analysis included 350 metastatic triple-negative breast cancer (mTNBC) patients who received first-line platinum-based chemotherapy at Fudan University Shanghai Cancer Center from November 2007 to July 2022. Patients were categorized into HER2-0 and HER2-low groups based on their HER2 status. Baseline clinicopathological characteristics, evolution of HER2 status between primary and metastatic lesions, and treatment efficacy were compared between the two groups.

Among the 350 mTNBC patients, 34.9% (122/350) were HER2-low and 65.1% (228/350) were HER2-0. Significant differences were observed between HER2-low and HER2-0 patients in terms of age and menopausal status. HER2-low patients were older (54 vs. 49 years, p=0.002) and had a lower proportion of premenopausal patients (32.8% vs. 52.6%, p<0.001) compared to HER2-0 patients. No significant differences were observed in progression-free survival (PFS) and overall survival (OS) between HER2-low and HER2-0 patients receiving first-line platinum-based chemotherapy (mPFS: 7.43 vs. 8.30 months, p=0.389, HR=1.11, 95% CI 0.88-1.40; mOS: 25.37 vs. 26.63 months, p=0.907, HR=1.02, 95% CI 0.76-1.37). Additionally, 32.3% (41/127) of patients exhibited discordant HER2 status between primary and metastatic lesions, primarily evolving from HER2-0 to HER2-low. Notably, patients with discordant HER2 status had significantly longer PFS compared to those with concordant status (mPFS: 11.07 vs. 7.53 months, p=0.020). The Cox multivariate analysis showed that HER2 status consistency (p=0.026) was an independent predictor of PFS.

In mTNBC patients, those with HER2-low status had similar responses to platinum-based chemotherapy as HER2-0 patients. There was significant discordance in HER2 status between primary and metastatic lesions. Patients with discordant HER2 status had better responses to platinum-based chemotherapy. Therefore, for patients with HER2-0 primary lesions, re-evaluation of HER2 status in metastatic lesions through biopsy may offer new treatment opportunities.

Until recently, targeted therapies have failed to benefit patients with human epidermal growth factor receptor 2 (HER2)-low-expressing breast cancer (BC). Nevertheless, antibody-drug conjugates (ADCs) have reshaped their prognosis.

We performed a systematic review and meta-analysis to assess the effectiveness of ADCs in patients with HER2-low advanced/metastatic (a/m) BC.

This study is a systematic review and meta-analysis.

We searched PubMed, Embase, and Cochrane databases as well as the American Society of Clinical Oncology, European Society for Medical Oncology, and San Antonio Breast Cancer Symposium conference proceedings.

Studies evaluating ADCs (trastuzumab deruxtecan (T-DXd), sacituzumab govitecan (SG), MRG002, and RC48-ADC) in patients with HER2-low a/mBC were included. We used R software (v.4.2.2) and random effects models for all analyses. Heterogeneity was assessed using the I 2 test.

Overall, 14 studies were included (five real-world studies and nine clinical trials (CTs)), with 2883 HER2-low a/mBC patients: 808 received treatment of physician's choice (TPC), and 2075 ADCs. Most were treated with T-DXd (n = 1691), followed by SG (n = 310), MRG002 (n = 56), and RC48-ADC (n = 18). Patients treated with T-DXd achieved a significantly higher objective response rate (ORR), disease control rate (DCR), and clinical benefit rate (CBR) than those receiving other ADCs. In the pooled analysis of four randomized CTs, ADCs statistically prolonged progression-free survival (n = 1828, hazard ratio (HR) 0.50, 95% confidence interval (CI) 0.36-0.68, I 2 = 82%, p < 0.001) and overall survival (n = 1546, HR 0.70, 95% CI 0.57-0.86, I 2 = 43%, p < 0.001) compared with TPC. Patients on ADCs also achieved a greater antitumor response than TPC, including better ORR (odds ratio (OR), 3.7, 95% CI 2.5-5.6, I 2 = 59%, p < 0.001), DCR (OR, 2.7, 95% CI 2.1-3.5, I 2 = 0%, p < 0.001), and CBR (OR, 3.6, 95% CI 2.6-5.2, I 2 = 56%, p < 0.01).

Our systematic review and meta-analysis confirms the efficacy of ADCs in HER2-low a/m BC patients over TPC. Future studies should focus on bringing ADCs into earlier lines of therapy in this population.

This study was registered in PROSPERO (CRD42024452962).

Antibody-drug conjugates (ADC) represent one of the most rapidly expanding treatment modalities in oncology, with 11 ADCs approved by the FDA and more than 210 currently being tested in clinical trials. Spanning over 40 years, ADC clinical development has enhanced our understanding of the multifaceted mechanisms of action for this class of therapeutics. In this article, we discuss key insights into the toxicity, efficacy, stability, distribution, and fate of ADCs. Furthermore, we highlight ongoing challenges related to their clinical optimization, the development of rational sequencing strategies, and the identification of predictive biomarkers. Significance: The development and utilization of ADCs have allowed for relevant improvements in the prognosis of multiple cancer types. Concomitantly, the rise of ADCs in oncology has produced several challenges, including the prediction of their activity, their utilization in sequence, and minimization of their side effects, that still too often resemble those of the cytotoxic molecule that they carry. In this review, we retrace 40 years of development in the field of ADCs and delve deep into the mechanisms of action of these complex therapeutics and reasons behind the many achievements and failures observed in the field to date.

Human epidermal growth factor receptor 2 (HER2)-low has emerged as a potential new entity in breast cancer (BC). Data on this subset are limited, and prognostic results are controversial, evidencing the need of further data in a BC real-world cohort.

Patients with HER2-negative stage I-III BC diagnosed between 2006 and 2016 were retrospectively reviewed in a single cohort from the Catalan Institute of Oncology Badalona. Demographics and clinicopathological characteristics were examined via medical charts/electronic health records. We aim to describe and compare HER2-0/HER2-low populations through Chi-square or Fisher test, and explore its prognostic impact using Kaplan-Meier curves and Cox regression models.

From a cohort of 1755 BC patients, 1401 invasive HER2-negative, stage I-III cases were evaluated. 87% were hormone receptor (HR)-positive versus 13% triple negative (TNBC). Overall, 43% were HER2-0 and 57% HER2-low (61% immunohistochemistry (IHC) 1+ and 39% IHC 2+). Comparing HER2-low versus HER2-0, HER2-low showed higher proportion of estrogen receptor (ER)-positive (91.6% vs 79.9%, p ⩽ 0.001) and progesterone receptor (PR)-positive (79.8% vs 68.9%, p ⩽ 0.001) cases. HER2-0 exhibited higher proportion of TNBC (20.1% vs 8.4%, p = 0.001), grade III tumors (28.8% vs 23.5%, p = 0.039), and higher Ki67 median value (26.47% vs 23.88%, p = 0.041). HER2-low was associated with longer time to distant recurrence (TTDR) compared to HER2-0 (67.8 vs 54.1 months; p = 0.015) and better BC-related survival (19.2 vs 16.3 years; p = 0.033). In the multivariable analysis, HER2-low was not an independent prognostic factor for TTDR and BC-related survival. ER expression showed a strong association with longer TTDR (Hazard Ratio: 0.425, p ⩽ 0.001) and improved BC-related survival (Hazard Ratio: 0.380, p ⩽ 0.001). PR expression was also associated with longer TTDR (Hazard Ratio: 0.496, p ⩽ 0.001), and improved BC-related survival (Hazard Ratio: 0.488, p ⩽ 0.001). Histological grade III was significantly associated with shorter TTDR (Hazard Ratio: 1.737, p = 0.002). Positive nodal status was the strongest factor correlated with worse BC-related survival (Hazard Ratio: 2.747, p ⩽ 0.001).

HER2-low was significantly associated with HR-positive disease, whereas HER2-0 group had higher incidence of TNBC, histological grade III and higher Ki67%. Although HER2-low group was associated with longer TTDR and improved BC-related survival, these findings could be explained by the greater proportion of favorable prognostic features in this subgroup compared to HER2-0.

Cancer is a significant health challenge globally, with millions of people affected every year, resulting in high morbidity and mortality. Although other treatment options are available with limitations, chemotherapy, either standalone or combined with other therapeutic procedures, is the most commonly used practice of treating cancer. In chemotherapy, cancer cells/malignant tumors are targeted; however, due to less target specificity, along with malignant cells, normal cells are also affected, which leads to various off-target effects (side effects) that impact the patient quality of life. Out of all the different types of cancers, breast cancer is the most common type of cancer in humans worldwide. Current anticancer drug discovery research aims to develop therapeutics with higher potency and lower toxicity, which is only possible through target-specific therapy. Antibody-drug conjugates (ADCs) are explicitly designed to target malignant tumors and minimize off-target effects by reducing systemic cytotoxicity. Several ADCs have been approved for clinical use and have shown moderate to good efficacy so far. Considering various aspects, chemotherapy and ADCs are useful in treating cancer. However, ADCs provide a more focused and less toxic approach, which is especially helpful in cases where resistance to chemotherapy (drug resistance) occurs and in the type of malignancies in which specific antigens are overexpressed. Ongoing ADC research aims to develop more target-specific cancer treatments. In short, this study presents a concise overview of ADCs specific to breast cancer treatment. This study provides insight into the classifications, mechanisms of action, structural aspects, and clinical trial phases (current status) of these chemo-biologic drugs (ADCs).

Bidirectional crosstalk between HER2 and estrogen receptor (ER) pathways may influence outcomes and the efficacy of endocrine therapy (ET). Low HER2 expression levels (HER2-low) have emerged as a predictive biomarker in patients with breast cancer (BC).

PALLAS is an open, international, phase 3 study evaluating the addition of palbociclib for 2 years to adjuvant ET in patients with stage II-III ER-positive/HER2-negative BC. To assess the impact of HER2 expression on patient outcomes in the phase III PALLAS trial, we analyzed (1) the association between rate of HER2-low with demographic and clinicopathological parameters, (2) the prognostic value of HER2-low status on invasive disease-free survival (iDFS), distant relapse-free survival (DRFS), and overall survival (OS) and (3) HER2 expression's value as a predictive biomarker of response to palbociclib. HER2-low was defined as HER2 immunohistochemistry (IHC) 1 + or IHC 2 + with negative in situ hybridization (ISH). All pathologic evaluation was performed locally. Prognostic and predictive power of HER2 were assessed with Cox models.

From the original PALLAS intention-to-treat population (N = 5753), 5304 patients (92.2%) were included in this analysis. Among these, 2254 patients (42.5%) were classified as having HER2 IHC 0 (HER2-0), and 3050 (57.5%) as having HER2-low disease (1838 with IHC 1 + and 1212 with IHC 2 +). Median follow-up was 59.8 months. HER2-low prevalence varied significantly across 21 participating countries (range 16.7% to 75.6%; p < 0.001) and was more frequent in patients enrolled in North America (63.1%) than in Europe (53.4%) or other regions (53.4%) (p < 0.001). HER2 status was not significantly associated with iDFS in a multivariable Cox model (hazard ratio 0.93, 95% confidence interval 0.81 - 1.06). No significant interaction was observed between treatment arm and HER2 status for iDFS (p = 0.43). Similar results were obtained for DRFS and OS.

In this large, prospective, global patient cohort, no differences were observed in clinical parameters, prognosis, or differential benefit from palbociclib between HER2-0 and HER2-low tumors. Significant geographic variability was observed in the prevalence of HER2-low status, suggesting a high degree of variation in pathologic assessment of HER2 expression without impact on outcomes.

Antibody-drug conjugates (ADCs) have recently emerged as a promising therapeutic option that combine the specificity of monoclonal antibodies and the cytotoxic effect of chemotherapy. With numerous ADCs approved and on the market, a particular concern of ADCs that target HER-2 has been their cardiac side effects, in view of the crucial role of HER-2 in cardiac development and physiology. While rarely toxic and generally safe, numerous publications have outlined the consistent association of trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd) with the development of cardiac toxicity. Despite not being clinically relevant in most cases, cardiac baseline evaluation, monitoring and early detection of cardiac adverse events remain pivotal with HER-2 targeting ADCs. This review aims to summarize and better characterize the complete cardiac toxicity profile of HER-2 ADCs, with the goal of improving clinical understanding of this adverse event, leading to better recognition, monitoring and management.

A next generation multiscale quantitative systems pharmacology (QSP) model for antibody drug conjugates (ADCs) is presented, for preclinical to clinical translation of ADC efficacy. Two HER2 ADCs (trastuzumab-DM1 and trastuzumab-DXd) were used for model development, calibration, and validation. The model integrates drug specific experimental data including in vitro cellular disposition data, pharmacokinetic (PK) and tumor growth inhibition (TGI) data for T-DM1 and T-DXd, as well as system specific data such as properties of HER2, tumor growth rates, and volumes. The model incorporates mechanistic detail at the intracellular level, to account for different mechanisms of ADC processing and payload release. It describes the disposition of the ADC, antibody, and payload inside and outside of the tumor, including binding to off-tumor, on-target sinks. The resulting multiscale PK model predicts plasma and tumor concentrations of ADC and payload. Tumor payload concentrations predicted by the model were linked to a TGI model and used to describe responses following ADC administration to xenograft mice. The model was translated to humans and virtual clinical trial simulations were performed that successfully predicted progression free survival response for T-DM1 and T-DXd for the treatment of HER2+ metastatic breast cancer, including differential efficacy based upon HER2 expression status. In conclusion, the presented model is a step toward a platform QSP model and strategy for ADCs, integrating multiple types of data and knowledge to predict ADC efficacy. The model has potential application to facilitate ADC design, lead candidate selection, and clinical dosing schedule optimization.

Antibody-drug conjugates (ADCs) consist of antibodies, linkers and payloads. They offer targeted delivery of potent cytotoxic drugs to tumor cells, minimizing off-target effects. However, the therapeutic efficacy of ADCs is compromised by heterogeneity in the drug-to-antibody ratio (DAR), which impacts both cytotoxicity and pharmacokinetics (PK). Additionally, the emergence of drug resistance poses significant challenges to the clinical advancement of ADCs. To overcome these limitations, a variety of strategies have been developed, including the design of multi-specific drugs with accurate DAR. This review critically summarizes the current challenges faced by ADCs, categorizing key issues and evaluating various innovative solutions. We provide an in-depth analysis of the latest methodologies for achieving homogeneous DAR and explore design strategies for multi-specific drugs aimed at combating drug resistance. Our discussion offers a current perspective on the advancements made in refining ADC technologies, with an emphasis on enhancing therapeutic outcomes.

Antibody-drug conjugates (ADCs) consist of monoclonal antibodies that target tumor cells and cytotoxic drugs linked through linkers. By leveraging antibodies' targeting properties, ADCs deliver cytotoxic drugs into tumor cells via endocytosis after identifying the tumor antigen. This precise method aims to kill tumor cells selectively while minimizing harm to normal cells, offering safe and effective therapeutic benefits. Recent years have seen significant progress in antitumor treatment with ADC development, providing patients with new and potent treatment options. With over 300 ADCs explored for various tumor indications and some already approved for clinical use, challenges such as resistance due to factors like antigen expression, ADC processing, and payload have emerged. This review aims to outline the history of ADC development, their structure, mechanism of action, recent composition advancements, target selection, completed and ongoing clinical trials, resistance mechanisms, and intervention strategies. Additionally, it will delve into the potential of ADCs with novel markers, linkers, payloads, and innovative action mechanisms to enhance cancer treatment options. The evolution of ADCs has also led to the emergence of combination therapy as a new therapeutic approach to improve drug efficacy.

Human epidermal growth factor receptor 2 (HER2)-low breast cancer (BC) is a new entity considered a biologically distinct subtype from HER2-zero BC. However, the importance of HER2 low expression on the activity of cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) remains unclear.

We conducted a single-center retrospective study including hormone receptor-positive (HR +) /HER2- metastatic BC (mBC) patients treated with CDK4/6i plus endocrine treatment (ET) as first-line therapy. Clinical outcomes were analyzed according to HER2 expression.

258 women were analyzed with a median follow-up of 25.4 months; 39.9% had HER2 low, and 60.1% had HER2 zero BC. Median progression-free survival (mPFS) in the HER2-low group was 27.6 months compared with 44.3 months in the HER2-zero group (p = 0.341). In patients receiving ribociclib, the mPFS in the HER2-low group was 24.2 months compared with 53.1 months in the HER2-zero group (multivariate-adjusted HR: 1.981, 95 Cl 1.094-3.586; p = 0.024). The survival probabilities at 24, 36 and 48 months for the HER2 low and HER2 zero groups were 82%, 69%, 69% and 83%, 75% and 69%, respectively (p = 0.336). Objective response rate (p = 0.179) and disease control rate (p = 0.338) did not significantly differ between HER-2-low and HER-2-zero groups.

The mPFS in the Her2-zero group was almost twice that of the Her2-low group, but the difference was not statistically significant. mPFS was significantly longer in the HER2-zero group compared to the HER2-low group in patients receiving ribociclib. More prospective studies are needed to understand the actual consequences of this biomarker.

Breast cancer is a heterogeneous disease, and its subtypes are characterized by hormone receptor and human epidermal growth factor receptor 2 (HER2) expression status. "HER2-low" tumors, which exhibit a low level of HER2 expression (immunohistochemistry 1+ or 2+ without gene amplification), were conventionally considered not amenable to anti-HER2 targeting agents based on the results of a phase III trial of trastuzumab. However, this perspective is being challenged by the emergence of novel anti-HER2 antibody-drug conjugates, such as trastuzumab-deruxtecan. These innovative therapies have demonstrated remarkable efficacy against HER2-low breast cancer, shedding new light on a previously overlooked category of breast cancer. Such promising results highlight the need for in-depth investigations of the biology and prognostic implications of HER2-low tumors. In this review, we comprehensively summarize the current evidence surrounding this topic and highlight areas that warrant further exploration and research in the future.

Breast cancer remains one of the predominant malignancies worldwide. In the context of inoperable advanced or metastatic human epidermal growth factor receptor 2 (HER2)-positive breast cancer, systemic management primarily relies on HER2-targeting monoclonal antibodies. With the successful development of anti-HER2 antibody-drug conjugates (ADCs), these agents have been increasingly integrated into therapeutic regimens for metastatic breast cancer. Here, we present the case of a 42-year-old female patient with HER2-positive pulmonary metastatic breast cancer who underwent an extensive treatment protocol. This protocol included chemotherapy, radiation therapy, hormonal therapy, surgical intervention on the breast, and anti-HER2 therapies. The anti-HER2 therapies involved both singular and dual targeting strategies using trastuzumab and the ADC disitamab vedotin (RC48) over an 8-year period. After experiencing disease progression following HER2-targeted therapy with RC48, the patient achieved noticeable partial remission through a therapeutic regimen that combined trastuzumab deruxtecan (DS8201) and tislelizumab. The data suggest a promising role for DS8201 in managing advanced stages of HER2-amplified metastatic breast cancer, especially in cases that demonstrate progression after initial HER2-directed therapies using ADCs. Furthermore, its combination with anti-PD-1 agents enhances therapeutic efficacy by augmenting the anti-tumoral immune response.

Trastuzumab deruxtecan (T-DXd; DS-8201; ENHERTU®) is a human epithelial growth factor receptor 2 (HER2)-directed antibody drug conjugate (ADC) with demonstrated antitumor activity against a range of tumor types. Aiming to understand the relationship between antigen expression and downstream efficacy outcomes, T-DXd was administered in tumor-bearing mice carrying NCI-N87, Capan-1, JIMT-1, and MDA-MB-468 xenografts, characterized by varying HER2 levels. Plasma pharmacokinetics (PK) of total antibody, T-DXd, and released DXd and tumor concentrations of released DXd were evaluated, in addition to monitoring γΗ2AX and pRAD50 pharmacodynamic (PD) response. A positive relationship was observed between released DXd concentrations in tumor and HER2 expression, with NCI-N87 xenografts characterized by the highest exposures compared to the remaining cell lines. γΗ2AX and pRAD50 demonstrated a sustained increase over several days occurring with a time delay relative to tumoral-released DXd concentrations. In vitro investigations of cell-based DXd disposition facilitated the characterization of DXd kinetics across tumor cells. These outputs were incorporated into a mechanistic mathematical model, utilized to describe PK/PD trends. The model captured plasma PK across dosing arms as well as tumor PK in NCI-N87, Capan-1, and MDA-MB-468 models; tumor concentrations in JIMT-1 xenografts required additional parameter adjustments reflective of complex receptor dynamics. γΗ2AX longitudinal trends were well characterized via a unified PD model implemented across xenografts demonstrating the robustness of measured PD trends. This work supports the application of a mechanistic model as a quantitative tool, reliably projecting tumor payload concentrations upon T-DXd administration, as the first step towards preclinical-to-clinical translation.

Antibody-drug conjugates (ADCs) have reshaped the cancer treatment landscape across a variety of different tumor types. ADCs' peculiar pharmacologic design combines the cytotoxic properties of chemotherapeutic agents with the selectivity of targeted therapies. At present, the approval of many ADCs used in clinical practice has not always been biomarker-driven. Indeed, predicting ADCs' activity and toxicity through the demonstration of specific biomarkers is still a great unmet need, and the identification of patients who can derive significant benefit from treatment with ADCs may often be uncertain. With the lack of robust predictive biomarkers to anticipate primary, intrinsic resistance to ADCs and no consolidated biomarkers to aid in the early identification of treatment resistance (ie, acquired resistance), the determination of precise biologic mechanisms of ADC activity and safety becomes priority in the quest for better patient-centric outcomes. Of great relevance, whether the target antigen expression is a determinant of ADCs' primary activity is still to be clarified, and available data remain quite controversial. Antigen expression assessment is typically performed on tissue biopsy, hence only providing information on a specific tumor site, therefore unable to capture heterogeneous patterns of tumor antigen expression. Quantifying the expression of the target antigen across all tumor sites would help better understand tumor heterogeneity, whereas molecularly characterizing tumor-intrinsic features over time might provide information on resistance mechanisms. In addition, toxicity can represent a critical concern, since most ADCs have a safety profile that resembles that of chemotherapies, with often unique adverse events requiring special management, possibly because of the differential in pharmacokinetics between the small-molecule agent versus payload of a similar class (eg, deruxtecan conjugate-related interstitial lung disease). As such, the identification of robust predictive biomarkers of safety and activity of ADCs has the potential to improve patient selection and enrich the population of patients most likely to derive a substantial clinical benefit, especially in those disease settings where different ADCs happen to be approved in competing clinical indications, with undefined biomarkers to make precise decision making and unclear data on how to sequence ADCs. At this point, the identification of clinically actionable biomarkers in the space of ADCs remains a top research priority.

The promising efficacy of novel anti-HER2 antibody-drug conjugates (ADC) in HER2-low breast cancer has made HER2-low a research hotspot. However, controversy remains regarding the neoadjuvant chemotherapy (NAC) efficacy, prognosis, and the relationship with hormone receptor (HR) status of HER2-low.

A retrospective analysis was conducted on 975 patients with HER2-negative breast cancer undergoing NAC at Tianjin Medical University Cancer Institute and Hospital, evaluating pathological complete response (pCR) rate and prognosis between HER2-low and HER2-zero in the overall cohort and subgroups.

Overall, 579 (59.4%) and 396 (40.6%) patients were HER2-low and HER2-zero disease, respectively. Compared with HER2-zero, the HER2-low cohort consists of more postmenopausal patients, with lower histological grade and higher HR positivity. In the HR-positive subgroup, HER2-low cases remain to exhibit lower histological grade, while in the HR-negative subgroup, they show higher grade. The HER2-low group had lower pCR rates than the HER2-zero group (16.4% vs. 24.0%). In the HR-positive subgroup, HER2-low consistently showed lower pCR rate (8.1% vs. 15.5%), and served as an independent suppressive factor for the pCR rate. However, no significant difference was observed in the pCR rates between HER2-low and HER2-zero in the HR-negative breast cancer. In the entire cohort and in stratified subgroups based on HR and pCR statuses, no difference in disease-free survival were observed between HER2-low and HER2-zero.

In the Chinese population, HER2-low breast cancer exhibits distinct characteristics and efficacy of NAC in different HR subgroups. Its reduced pCR rate in HR-positive subgroup is particularly important for clinical decisions. However, HER2-low is not a reliable factor for assessing long-term survival outcomes.

Anti-human epidermal growth factor receptor 2 (HER2) agents have exhibited pronounced tumor-inhibitory activity, yet the accompanying ocular toxicity has frequently been underestimated. We aim to conduct a comprehensive comparative analysis of ocular toxicity risk related to various anti-HER2 agents. We executed a retrospective pharmacovigilance investigation based on the FDA Adverse Event Reporting System (FAERS) database, covering the period from Q2 2018 to Q1 2023. The disproportionality analysis was performed to assess ocular toxicity risk. Multivariate logistic regression was implemented to mitigate potential biases. Moreover, the time to onset of ocular toxicity was also evaluated. A total of 3467 ocular adverse event (AE) reports concerning anti-HER2 agents were collected. At the preferred term (PT) level, there were 69 positive signals, among which excessive eye blinking, abnormal sensation in the eye, and asthenopia presented a significant risk. In comparison to tyrosine kinase inhibitors (TKIs), antibody drugs were associated with a broader range of ocular disorders at Standardized MedDRA Queries (SMQ)levels, including conjunctival disorders, corneal disorders, ocular infections, ocular motility disorders, optic nerve disorders, and retinal disorders. In terms of onset time, pertuzumab displayed an earlier onset at 21.5 days, while trastuzumab deruxtecan had the latest at 91.5 days. In summary, our study reveals varying degrees of ocular toxicity related to anti-HER2 agents, with a significantly higher risk observed in antibody drugs. Additionally, novel ocular toxicity signals, not documented in product labels, have been detected. In the future, further research will be necessary to validate our findings.

Trastuzumab emtansine (T-DM1) has been approved worldwide for treating metastatic breast cancer (mBC) in patients who have received first-line therapy, shown disease progression, and are human epidermal growth factor receptor 2 (HER2)-positive. T-DM1 received approval in China to treat early-stage breast cancer (BC) in 2020 and for mBC in 2021. In March 2023, T-DM1 was included in medical insurance coverage, significantly expanding the eligible population.

This post-marketing observational study aimed to assess the safety and effectiveness of T-DM1 in real-world clinical practice in China. This study enrolled 31 individuals with HER2-positive early-stage BC and 70 individuals with HER2-positive advanced BC from 8 study centers in Shandong Province, China. The T-DM1 dosage was 3.6 mg/kg injected intravenously every 3 weeks until the disease advanced or the drug toxicity became uncontrollable, whichever occurred earlier. Additionally, efficacy and safety information on T-DM1 were collected.

During the 7-month follow-up period, no recurrence or metastases were observed in patients who had early-stage BC. The disease control rate was 31.43% (22/70) in patients with advanced BC. The most common adverse effect of T-DM1 was thrombocytopenia, with an incidence of 69.31% (70/101), and the probability of Grade ≥ 3 thrombocytopenia was 11.88% (12/101).

This real-world study demonstrated that T-DM1 had good efficacy and was well tolerated by both HER2-positive early-stage BC and mBC patients.

Antibody-drug conjugates (ADCs)-a groundbreaking class of agents for targeted oncological therapies-consist of monoclonal antibodies with strong antigenic specificity coupled with highly active cytotoxic agents (also referred to as "payloads"). Over the past 2 decades, breast cancer research has evolved into a focal point for the research and development of ADCs, leading to several recent landmark publications. These advancements are ushering in a transformative era in breast cancer treatment and redefining conventional classifications by introducing a prospective subtype termed "HER2-low." The latest iterations of ADCs have demonstrated enhanced efficacy in disease management through the optimization of various factors, notably the incorporation of the bystander effect. These conjugates are no longer limited to the oncogenic driver human epidermal growth factor receptor 2 (HER2). Other antigens, including human epidermal growth factor receptor 3 (HER3), trophoblast cell surface antigen 2 (Trop-2), zinc transporter ZIP6 (LIV-1), and folate receptor α (FRα), have recently emerged as intriguing tumor cell surface nondriver gene targets for ADCs, each with one or more specific ADCs that showed encouraging results in the breast cancer field. This article reviews recent advances in the application of ADCs in the treatment of HER2-low breast cancer. Additionally, this review explores the underlying factors contributing to the impact of target selection on ADC efficacy to provide new insights for optimizing the clinical application of ADCs in individuals with low HER2 expression in advanced breast cancer.

Numerous studies have reported the efficacy of antibody-drug conjugates (ADCs) for treating breast cancer. However, during cytotoxic drug treatment, long-term disabling fatigue is common. Moreover, studies in the relevant literature have indicated that fatigue can significantly increase the incidence of depression and sleep disorders. Therefore, this meta-analysis aims to evaluate the incidence of fatigue in breast cancer survivors treated with ADCs.

PubMed, EMBASE, Web of Science, and Cochrane Library databases were systematically searched for articles and conference abstracts published before March 16, 2023. Further, two authors independently extracted data from the included studies. The primary outcome of this study was the incidence of all-grade fatigue caused by the use of ADCs in patients with breast cancer. Finally, a random-effects model was used to calculate the incidence and 95% confidence intervals (CIs) of the outcome.

Overall, 7963 patients from 31 studies were included in this meta-analysis to assess the incidence of fatigue caused by the use of approved and marketed ADCs in patients with breast cancer. Notably, the incidence of all-grade fatigue during ADC monotherapy was 39.84% (95% CI, 35.09%-44.69%). In subgroup analyses, among ADCs, the incidence of trastuzumab deruxtecan-induced fatigue was the highest, with an all-grade fatigue incidence of 47.05% (95% CI, 42.38%-51.75%). Meanwhile, the incidence of trastuzumab emtansine (T-DM1)-induced all-grade fatigue was 35.17% (95% CI, 28.87%-41.74%), which was the lowest among ADCs. Further, the incidence of all-grade fatigue due to sacituzumab govitecan was 42.82% (95% CI, 34.54%-51.32%), which was higher than that due to T-DM1. Moreover, the incidence of fatigue was higher with T-DM1 combination therapy than with monotherapy.

Clinicians have highlighted the high incidence of ADC-related fatigue and its negative impact on patients' physical and mental health, making fatigue an important research variable. The results of this study will further contribute to a comprehensive understanding of ADCs, which have some clinical importance and are of great benefit to patients with breast cancer.

Approximately 60% of traditionally defined human epidermal growth factor receptor 2 (HER2)-negative breast cancers express low levels of HER2 [HER2-low; defined as immunohistochemistry (IHC) 1+ or IHC 2+/in situ hybridization (ISH)-]. HER2-low breast cancers encompass a large percentage of both hormone receptor-positive (up to 85%) and triple-negative (up to 63%) breast cancers. The DESTINY-Breast04 trial established that HER2-low tumors are targetable, leading to the approval of trastuzumab deruxtecan (T-DXd) as the first HER2-directed therapy for the treatment of HER2-low breast cancer in the United States and Europe. This change in the clinical landscape results in a number of questions and challenges-including those related to HER2 assessment and patient identification-and highlights the need for careful assessment of HER2 expression to identify patients eligible for T-DXd. This review provides context for understanding how to identify patients with HER2-low breast cancer with respect to sample types, scoring and reporting HER2 status, and testing methods and assays. It also discusses management of important T-DXd-related adverse events. Available evidence supports the efficacy of T-DXd in patients with any history of IHC 1+ or IHC 2+/ISH- scores; however, future research may further refine the population who could benefit from T-DXd or other HER2-directed therapies and identify novel methods for patient identification. Because HER2 expression can change with disease progression or treatment, and variability exists in scoring and interpretation of HER2 status, careful re-evaluation in certain scenarios may help to identify more patients who may benefit from T-DXd.

Circulating tumor cells (CTCs) are the seeds of distant metastases of malignant tumors and are associated with malignancy and risk of metastasis. However, tumor cells undergo epithelial-mesenchymal transition (EMT) during metastasis, leading to the emergence of different types of CTCs. Real-time dynamic molecular and functional typing of CTCs is necessary to precisely guide personalized treatment. Most CTC detection systems are based on epithelial markers that may fail to detect EMT CTCs. Therefore, it is clinically important to identify new markers of different CTC types. In this study, bioinformatics analysis and experimental assays showed that trophoblast cell surface antigen 2 (TROP2), a target molecule for advanced palliative treatment of triple-negative breast cancer (TNBC), was highly expressed in TNBC tissues and tumor cells. Furthermore, TROP2 can promote the migration and invasion of TNBC cells by upregulating EMT markers. The specificity and potential of TROP2 as an EMT-associated marker of TNBC CTCs were evaluated by flow cytometry, immunofluorescence, spiking experiments, and a well-established CTC assay. The results indicated that TROP2 is a potential novel CTC marker associated with EMT, providing a basis for more efficacious markers that encompass CTC heterogeneity in patients with TNBC.