Bacteria in neoplastic diseases: A brief note on Wilms tumor

Abstract

Bacteria can be involved in the pathological processes of cancer in different manners - for instance, as an etiological factor or predisposing factor, in secondary infection, as well as modified bacteria or bacterial products in cancer treatment. The bacterial etiological connection or its role as a predisposing factor is mainly relevant to adult cancers, which are primarily associated with individual lifestyles and/or environmental issues. In contrast, genetic abnormalities are perhaps linked with tumorigenesis in the pediatric age group. Nonetheless, secondary infections significantly affect morbidity and mortality among pediatric cancer patients in spite of precautionary measures. On the other hand, bacterial products, i.e., toxins, are potential molecules for targeted cancer therapy. These therapeutic agents have two parts: Usually a receptor-binding antibody (e.g., anti-HER2 antibody) and a toxin (e.g., Pseudomonas exotoxin A). Similarly, several investigators have been trying to develop therapeutic approaches that target Wilms tumor 1 protein, whose dysregulation is thought to be fundamentally responsible for the pathogenesis of Wilms tumor, the most common kidney tumor of childhood. However, the overexpression of Wilms tumor 1 protein has been documented in many cancer tissues - both solid tumors and hematological malignancies. This article briefly reviews both the pathological and clinical characteristics of Wilms tumor along with relevant secondary infections.

Key Words: Bacteria; Cancer; Infectious complications; Wilms tumor; Wilms tumor 1 vaccine

Core Tip: This review describes different aspects of Wilms tumor, e.g., pathogenesis, epidemiology, immune responses, and complications, particularly secondary bacterial infections. The pertinent Wilms tumor 1 (WT1) gene and its protein play an important role in the embryogenesis of the kidney and the development of Wilms tumor. Interestingly, WT1 functions both as a tumor suppressor as well as an oncogenic factor, probably depending on the biological circumstances. Nevertheless, WT1 is overexpressed in several tumor tissues. For this reason, WT1-targeted strategies are potential areas in cancer therapy.

INTRODUCTION

Different bacterial species may contribute to the pathological processes of cancer through various mechanisms. Chronic inflammation triggered by Escherichia coli (E. coli) in inflammatory bowel disease is believed to predispose the risk of colon cancer[1]. Additionally, certain chronic bacterial infections have been linked to tumorigenesis, such as Helicobacter pylori (H. pylori) in cancer of the stomach, Salmonella typhi in cancer of the gallbladder, and Chlamydia pneumoniae in cancer of the lung. Bacteria-released metabolites or toxins, e.g., cytotoxin-associated gene A protein by H. pylori and colibactin by some members of Enterobacteriaceae, including E. coli, can promote malignancy by influencing pathways like the Wnt signaling pathway or sustaining inflammation. Notably, individuals infected with H. pylori may develop gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue lymphoma. It is worth mentioning that cancer patients are more susceptible to secondary bacterial infections, a significant cause of morbidity and mortality. Members of the Enterobacteriaceae like E. coli, Klebsiella spp., the Gram-negative bacillus Pseudomonas aeruginosa (P. aeruginosa), and the Gram-positive Staphylococcus aureus are frequently found in cancer patients[2].

Interestingly, Salmonella spp. within the Enterobacteriaceae family is thought to promote colon cancer but has also shown potential for anticancer properties. The Salmonella genome encodes various virulence factors that can impact a number of cancer-related intracellular signaling pathways, contributing to tumor development. However, attenuated Salmonella strains have been shown to colonize solid tumors in experimental models, inhibiting tumor growth[2,3]. In the same manner, P. aeruginosa poses a significant risk for secondary infections in cancer patients, yet its products could be exploited in anticancer therapy. Mechanisms involving P. aeruginosa include the utilization of bacterial toxins in targeted therapy, immune modulation by genetically modified strains carrying tumor antigen genes, and colonization of bacteria in hypoxic tumor regions, leading to cancer cell death. Virulence factors of P. aeruginosa, such as exotoxin, cyclodipeptides, and mannose-sensitive hemagglutinin, are under evaluation for their potential as anticancer therapeutic agents[4]. A comprehensive understanding of these virulence factors at the cellular and molecular levels is essential for addressing various pathological phenomena and exploring their therapeutic potential.

The aim of this study is to briefly describe the pathology of Wilms tumor and the role of relevant Wilms tumor 1 (WT1) from a bacteriological perspective. For this purpose, this review has made an effort to construct a narrative synthesis of pertinent findings from published literature that are available through commonly used databases such as MEDLINE/PubMed and Google Scholar. A search was conducted with different keywords, including “Wilms tumor” and “bacteria”, “chromosome 11” and “disease”, and “WT1 immunotherapy”. Special emphasis was given to collecting the recent literature, specifically from the past quinquennium, to display the current state of knowledge. All identified studies in the keyword search were manually evaluated for appropriateness.

BIOLOGICAL THERAPY IN CANCER: WILMS TUMOR 1 PROTEIN, IMMUNE RESPONSE, AND UTILIZATION OF THE BACTERIAL SYSTEM

Immunotherapy or biological therapy against cancer includes several types or methods, such as immune modulation by genetically modified bacteria, therapeutic cancer vaccines (that trigger patients’ immune mechanisms against certain tumor-related antigens), checkpoint inhibitors, and tumor antigen-targeting monoclonal antibody therapy. Some of these methods are currently practiced in the healthcare system, but many potential strategies are being investigated at various research phases/levels. Members of the epidermal growth factor receptor family, particularly HER2, are important antigens that have been commonly selected for the targeted therapy - for example, trastuzumab (a monoclonal antibody against HER2) or antibody-drug conjugate trastuzumab-emtansine (a microtubule inhibitor)[5]. Of note, HER2 is a transmembrane tyrosine kinase receptor and is overexpressed in many cancer cells. Although it is still in the experimental phase, trastuzumab could be conjugated with toxins of bacterial origin, such as Pseudomonas exotoxin A and Diphtheria toxin[6,7]. In a similar manner, bacteria could be utilized in different ways to target various molecules of cancer cells (Table 1)[8-14].

Table 1 Selected studies that utilized the bacterial system in targeted therapeutic strategies against cancer.

Ref.	Authors and brief study outline	Salient findings
Carroll et al[8]	This study had a few separate components, which included the intra-tumoral injection of killed mycobacteria (complete Freund’s adjuvant/CFA) in in vivo models, natural tumors in dogs (mastocytoma/mast cell tumor) and horses (melanoma), and patients with different advanced cancers from Switzerland and Australia (administered into primary or metastatic tumors). In female DBA/2 J mice, for tumor development, the following cells were injected: P815 (mouse mastocytoma) cells and 4T1 (mouse mammary adenocarcinoma) cells orthotopically, and CT26 (mouse colon carcinoma) cells subcutaneously	The efficacy of intra-tumoral CFA injection was observed in orthotopically injected P815 and 4T1 tumors but not in the non-orthotopically injected CT26 tumors. Out of 14 dogs, 3 dogs presented complete regression of their tumor and substantially extended survival in 2 cases. So, in dogs, 21% showed a complete response and an overall response for 35%. Among horses (n = 11), 3 horses (27%) exhibited the sign of clinical response (mass remission and reduction in size). CFA administration induced extensive infiltration of immune cells into the tumors in comparison to control (saline). Out of 8 patients, 5 showed substantial immune cell infiltration in tumor tissue along with extensive necrosis
Park et al[9]	This was a clinical study conducted in Korea; 19 patients with HPV-16 single infection and histologically confirmed CIN3 were included between 2014-April and 2016-March, and they were administered orally Lactobacillus casei that expressed HPV-16 E7 antigen on the surface. Phase 1 was a safety test, and phase 2a was an efficacy test, which finally included 8 women who were administered this bacterial agent (1000 mg) in weeks 1, 2, 4, and 8 (5 times a week)	There was a steady increase of HPV-16 E7-specific IgG level in plasma. Histological responses were assessed 7 weeks after the final medication. Clinical efficacy was observed in 6 patients (out of 8, 75%); complete remission to normal was seen in 3 women, and in the other 3 women, regression to CIN1 was noticed. There were no seriously observed adverse effects at 1000 mg administered dosage of this oral vaccine
Augustin et al[10]	This was an in vivo study that utilized BALB-neuT mice and a virulence-attenuated strain of Salmonella typhimurium for the colonization of tumors and the delivery of immunomodulators. The plasmids in the bacteria were designed to express IL-15 superagonist IL-15Ra-IL-15 (having anticancer efficiency) as well as anti-CTLA-4 and anti-PD-L1 (immune checkpoint inhibitors). BALB-neuT transgenic mouse model overexpresses HER2 and spontaneously develops mammary carcinoma. The investigators also used cannabidiol, a vascular disrupting agent, to create intra-tumoral necrotic spaces	In transgenic mice, the combination treatment regimen showed a statistically significant 64% slower tumor growth and a 25% increase in mean survival time in comparison to without treatment control mice. Furthermore, the experiments were completed with minimal toxicity, as assessed by less than 7% weight loss and a restoration of normal weight gain in 3 days after administration of the bacteria intravenously
Manuel et al[11]	In this in vivo study, KPC-luc pancreatic cancer cells were orthotopically implanted into the pancreas of C57BL/6 mice and treated with the combination of PEGPH20 and shIDO-ST. PEGPH20 diminishes hyaluronic acid in the tumor extracellular matrix, causing stromal remodeling, vascular reduction, and improved drug delivery, while shIDO-ST is a Salmonella typhimurium-based therapy targeting the immunosuppressive molecule indoleamine 2,3-dioxygenase	The study noticed extended survival and frequent total regression of tumors. Along with this type of response to the treatment, there was also migration and accumulation of activated neutrophils into tumors. Furthermore, CD8+ T cells were recorded to be associated with the late control of tumors. Following treatment, supportive care for animals was not required, and maintenance of normal body weight was noted
Hsieh et al[12]	The aim of this in vivo study was to determine the efficacy of Escherichia coli engineered to overexpress β-glucuronidase [E. coli (lux/βG)] in anticancer activity. Irinotecan (CPT-11) is used in chemotherapy for colon cancer and hydrolyzed into SN-38 (active form). SN-38 is rapidly metabolized to inactive glucuronide conjugate SN-38G. However, β-glucuronidase can enhance anti-tumor effectiveness by converting SN-38G into SN-38. NOD/SCID mice were inoculated subcutaneously with different colon cancer cells (HCT116, LS174T, and CT26). A single intravenous injection of E. coli was administered when the tumor size reached about 150 mm3	E. coli (lux/βG) could hydrolyze SN-38G to SN-38 and selectively accumulate in tumors. However, E. coli (lux/βG) did not efficiently enhance SN-38 anticancer activity in tumor xenografts in comparison to non-engineered E. coli. On the other hand, the incubation of SN-38G with E. coli (lux/βG) increased the inhibition of HCT116 cell growth by 135-fold. In addition, E. coli (lux/βG) can produce cytotoxic concentrations of SN-38 from SN-38G
Yamatsugu et al[13]	In this study (both in vitro and in vivo), antibody mimetic-drug conjugates based on high-affinity binding of mutated streptavidin and modified iminobiotin were used to target HER2-positive KPL-4 breast cancer cells and in KPL-4 xenograft model (BALB/cSlc-nu/nu nude mice). Antibody mimetics (i.e., non-immunoglobulin miniproteins or affibody molecules) were fused to a streptavidin variant, which was subsequently expressed in E. coli inclusion bodies	By utilizing bis-iminobiotin conjugated with photo-activating silicon phthalocyanine, the drug conjugates developed against HER2 successfully killed cancer cells. Moreover, the HER2-targeting antibody mimetic-drug conjugates were demonstrated to be useful for the in vivo xenograft model
Shahid et al[14]	This in vitro study utilized genetically engineered E. coli (E. coli BL21) that secretes a pore-forming toxin HlyE, and binds to HER2 receptors on JIMT-1 breast cancer cells by anti-HER2Rs15d nanobody. JIMT-1 cells are hormone receptor negative (both estrogen and progesterone receptors), amplified HER2 positive, and insensitive to trastuzumab	The results showed that the nanobody effectively bound to HER2-positive JIMT-1 cells in vitro, and E. coli BL21 killed the target cells with HlyE toxin, which was secreted by using the YebF secretion system (a type VI secretion system)

CFA: A potent immune stimulant that contains mineral oil, surfactant, and heat-killed Mycobacteria; CIN: Cervical intraepithelial neoplasia; HPV: Human papillomavirus; IL: Interleukin; Luc: Luciferase (firefly); Lux: Luciferase (bacterial); PEGPH20: PEGylated human recombinant PH20 hyaluronidase; E. coli: Escherichia coli; CTLA-4: Cytotoxic T lymphocyte-associated antigen-4; PD-L1: Programmed cell death ligand 1.

Like HER2-targeting therapy, efforts are continuing to utilize the WT1 protein in cancer treatment. The WT1 protein is an immunogenic and overexpressed tumor antigen[15]. Studies have shown a higher frequency of WT1 protein expression in various solid tumors and hematopoietic malignancies, e.g., rhabdomyosarcoma, melanoma, ovarian serous adenocarcinoma, renal cancer, acute lymphoblastic leukemia, and chronic myelogenous leukemia[16,17]. In general, it has been documented that the overexpression of WT1 indicates an unfavorable prognosis[18]. Interestingly, Wilms tumor 1-associating protein (WTAP), a nuclear protein (gene location: 6q25-27), has been found to interact with WT1, and the protein is overexpressed in several cancer cells, such as gastric cancer, ovarian cancer, and renal cell carcinoma - the upregulation of WTAP also displays poor prognosis, like WT1[19-22]. It is worth mentioning that in vertebrates, WTAP is conserved, especially in mammals and fish[23]. Furthermore, the involvement of WTAP in antiviral immunity has been documented in Miichthys miiuy, a species of fish found in coastal waters of the northwestern Pacific Ocean. On the other hand, regarding the body’s immune-related parameters, a recent study showed that kidney tumors, along with certain pediatric tumors such as neuroblastoma, lymphoma, and retinoblastoma, had higher blood levels of interferon-gamma, interleukin-12, tumor necrosis factor, and angiopoietin-2 in comparison to children with other solid tumors[24]. Moreover, elevated levels of cancer-associated fibroblasts were detected in Wilms tumors, which also displayed a significant positive association between two prognostically linked indicators, i.e., tumor mutation burden and CD8+ T cell abundance in tumors. Interestingly, the investigators of the study noticed a negative relationship between circulating CD8+ T cell levels and tumor-infiltrating CD8+ T cells that also appeared to be connected to plasma colony-stimulating factor 1, programmed cell death 1-ligand 2, TIE2 (a receptor for angiopoietin-1 and angiopoietin-2), and adenosine deaminase (involved in purine metabolism)[24].

There is a limited expression of WT1 in normal tissues compared to its overexpression in various malignant tumors[25]. Therefore, it is expected that this limited expression in normal tissues can decrease the possibility of adverse consequences during WT1-targeted immunotherapy. Nevertheless, regarding WT1-targeted immunotherapy, results of the preclinical and early-phase clinical trials in pancreatic cancer showed a potent antitumor effect when WT1-targeted cancer vaccines were administered along with chemotherapy[26]. Furthermore, an analysis of various clinical trials on advanced pancreatic cancer has observed that the adverse effects of WT1-targeted vaccines were not serious, and vaccines can be used safely in combination with chemotherapy/gemcitabine[27]. Similarly, a recent phase I/II clinical trial on WT1-mRNA dendritic cell vaccination recorded that it was immunogenic, safe, and suitable in clinical qualities among patients with advanced solid tumors[28].

In the aforementioned study, which was conducted in Belgium, vaccination with WT1 mRNA-electroporated autologous dendritic cells was feasible in 39 patients with advanced cancers such as glioblastoma multiforme (n = 13), metastatic breast cancer (n = 12), pleural mesothelioma (n = 10), and other tumors (n = 4)[28]. In general, median overall survival was roughly three and a half years, which is reasonable. One of the recently published reports used a similar method in 10 Korean patients with high-risk acute myelogenous leukemia[29]. In this study, patients received an allogeneic sibling donor hematopoietic stem cell transplantation followed by anti-leukemic WT1-specific cytotoxic T cells infusion. Of note, for the generation of WT1-specific cytotoxic T cells in vitro, dendritic cells were transduced with an adenoviral vector expressing WT1. After engraftment, three patients died due to relapse, one patient died at 10 months after transplant due to Gram-negative sepsis and a disseminated infection of herpes simplex virus, one patient died at 1 year due to septic pneumonia and gastrointestinal cytomegalovirus disease along with extensive-type graft-versus-host disease, and four patients developed chronic graft-versus-host disease. In another study in Japan, Nishida et al[30] used Bacillus Calmette-Guérin cell wall skeleton with WT1 peptide. It is worth mentioning that Bacillus Calmette-Guérin is the live attenuated form of Mycobacterium bovis, and Bacillus Calmette-Guérin cell wall skeleton is a strong immune adjuvant. This study included 18 patients with advanced cancers - melanoma (n = 7), colon (n = 5), hepatobiliary cancer (n = 4), ovary (n = 1), and lung (n = 1). These cancers overexpressed WT1 and were refractory to standard therapies. Overall, no serious treatment-related systemic adverse events were noticed. However, four patients developed different disorders such as gastrointestinal obstruction, motor paralysis, hypokalemia, and infections. Hepatobiliary infection was observed in two patients, and bladder infection in one patient.

Apart from commonly used WT1 peptide vaccines and dendritic cell-based vaccines in different clinical trials for WT1-targeted cancer immunotherapy, a group of Japanese scientists has developed a WT1 oral vaccine using genetically modified Bifidobacterium longum that delivers WT1 protein to the gut immune system[31,32]. It may be worth mentioning that Bifidobacterium longum is a rod-shaped Gram-positive bacterium, which colonizes our intestine and is thought to be associated with probiotic function. Through genetically modified Bifidobacterium, WT1 protein can be delivered to dendritic cells of Peyer's patches/intestinal lymphoid tissue and then presented to T-lymphocytes. Interestingly, the abovementioned reports documented that the oral WT1 vaccine in the mouse model displayed superior anti-cancer effects compared to the WT1 peptide vaccine, aside from the convenience of oral administration.

WT1 is ubiquitously expressed (possibly having both tumor-suppressive and oncogenic functions, depending on the conditions) and present at a high concentration in cancer cells. Therefore, WT1-targeted vaccines could be useful in the treatment of different cancers. In addition, high levels of expression perhaps reduce the possibility of antigen down-regulation during WT1-targeted immunotherapy. Clearly, comprehensive clinical studies could evaluate efficacy and safety precisely.

WILMS TUMOR: ETIOLOGICAL FACTORS AND SECONDARY INFECTIONS

Some of the common cancers in children and adolescents are acute lymphoblastic leukemia, lymphomas, retinoblastoma, medulloblastoma, rhabdomyosarcoma, Wilms tumor, and Ewing sarcoma. In general, pediatric cancers represent roughly 2% of all human malignancies. Unlike cancer development in adult people, which is mainly connected to lifestyle and can be prevented to a considerable extent, chromosomal or genetic aberrations and relevant alterations in signaling pathways perhaps play a crucial role in childhood cancers[33]. Obviously, these etiological factors in childhood cancers are difficult to mitigate. Nevertheless, responses to currently available treatment regimens for many pediatric cancers are promising.

Primary malignant tumors of the kidney account for up to 11% of pediatric cancers[34]. Among these tumors, the most common condition is Wilms tumor or nephroblastoma, which constitutes more than 90% of cases[35]. Other notable pediatric kidney tumors are malignant rhabdoid tumors (about 2% of renal tumors), clear cell sarcoma (2%-5%), and pediatric renal cell carcinoma (2%-6%)[33,36]. Generally, Wilms tumor is unilateral, although bilateral tumors have been documented in around 5%-8% of patients; bilateral tumors could be synchronous (occurring simultaneously) or metachronous (developing at different time points)[37]. It is worth mentioning that familial Wilms tumors are rare, and the development of Wilms tumor in adults is also a rare phenomenon[34,38]. Notably, pediatric patients with Wilms tumor often present with hypertension, hematuria, and vague abdominal pain. Wilms tumor is also a significant primary lesion for pulmonary metastases in children[39].

Wilms tumor is a classic example of a neoplasm that originates from the aberrant pathway of organogenesis. Human kidneys develop from the ureteric bud and the metanephric blastema (which forms the nephrons and stroma). Persistent undifferentiated blastema, i.e., the nephrogenic rest, could undergo malignant transformation, which is closely linked to the alterations on the p/short arm of chromosome 11[40] (Figures 1 and 2[41-43]). Inactivation of the tumor suppressor WT1 (located at 11p13) relates to the development of Wilms tumor along with other diseases such as WAGR syndrome, Denys-Drash syndrome, and Frasier syndrome[44]. In addition, Wilms tumor has been reported to be associated with a wide range of pathologies, e.g., childhood overgrowth syndromes such as Beckwith-Wiedemann syndrome (dysregulation of genes at chromosome 11p15) and isolated hemihypertrophy (hemihyperplasia, which could be connected with Beckwith-Wiedemann syndrome) as well as tumor predisposition syndromes such as biallelic BRCA2 mutations[45]. At the 11p15 region, the gene for the insulin-like growth factor 2 (IGF2/H19 domain) is located adjacent to the insulin gene. Abnormal expressions of IGF2 could be involved in the pathogenesis of Wilms tumor[46].

Figure 1 Schematic diagram of chromosome 11 and its short (p) arm-linked certain diseases. Aniridia: A pan-ocular disorder with partial or complete deficiency of the iris; Beckwith-Wiedemann syndrome: A congenital overgrowth disorder; Beta-hemoglobinopathies (defects in β-globin chains): Beta-thalassemia and Sickle cell disease; Congenital hyperinsulinism: Characterized by excess insulin secretion and profound hypoglycemia; Denys-Drash syndrome: A disorder with congenital nephropathy/diffuse glomerulosclerosis, Wilms tumor, gonadal dysgenesis and cryptorchidism (among male patients); Frasier syndrome: Associated with nephropathy/focal segmental glomerulosclerosis, and gonadal abnormalities that commonly become cancerous/gonadoblastoma (among male patients); Silver-Russell syndrome: Clinical features include growth restriction, body asymmetry, and relative macrocephaly (etiologies are not related to chromosome 11 in about 50% of cases); WAGR: Wilms tumor-aniridia-genitourinary abnormalities-mental retardation.

Figure 2 Schematic diagram of the Wilms tumor 1 gene and its encoded protein. The Wilms tumor 1 (WT1) gene has ten exons: Exons 1-6 encode the transcriptional regulation region that is rich in proline-glutamine (N-terminus side), and exons 7-10 encode the zinc finger region, which is the DNA-binding domain (C-terminus side). Based on the translation initiation sites and post-transcriptional processes such as alternative splicing and RNA modification, more than 30 WT1 isoforms can originate, for example, an insertion of 17 amino acids in exon 5, and an insertion of a tripeptide lysine-threonine-serine (KTS) between zinc fingers 3 and 4. Of note, the isoform without KTS can frequently bind to DNA to function as a transcriptional regulator. WT1 protein has a molecular weight of about 50 kDa, and it is associated with the development of several key body structures, e.g., the heart, blood vessels, lung, kidney, gonads, spleen, retina, and the nervous system. In adult humans, WT1 is overexpressed in podocytes. WT1 transcriptionally controls various genes, such as fibroblast growth factor genes, Pax2, SRY (crucial for the development of seminiferous tubules and testes), and NR5A1/SF1 (for adrenal-gonadal primordium survival). Interestingly, WT1 can control its own expression. In addition, by binding to the DNA sequence 5’-GCGGGGGCG-3’, WT1 can affect the transcription of many other genes, including epidermal growth factor, insulin-like growth factors and their receptors, platelet-derived growth factor A, transforming growth factor-β, and macrophage colony-stimulating factor. Similarly, WT1 is involved in the functioning of a number of signaling pathways, such as Wnt/β-catenin, NOTCH (the term originated from Drosophila melanogaster with notched wings), JAK/STAT (Janus kinase/signal transducer and activator of transcription), and retinoic acid signaling pathways[41-43]. KTS: Single-letter code of amino acids representation - lysine (K), threonine (T), and serine (S).

In general, prognosis in Wilms tumor cases has been documented to be better than pediatric patients with other kidney cancers such as renal cell carcinoma, malignant rhabdoid tumor, and clear cell sarcoma[47]. Although the overall prognosis is good in children with Wilms tumor, socioeconomic status perhaps has a great impact on the patient’s survival (Table 2)[47,48]. Poor overall survival includes conditions such as advanced-stage Wilms tumor, cases with metastasis, and particularly metastatic bilateral Wilms tumor[37,48]. On the other hand, cancer treatment regimens such as chemotherapy increase susceptibility to infections, predominantly by bacteria but also by fungi and viruses. Eventually, infection-related complications cause treatment-linked morbidity, mortality, and overall poor prognosis.

Table 2 Salient findings of recent studies that analyzed a considerable number of patients with Wilms tumor for prognostic characteristics.

Authors and brief study outline	Statistical significance of the results	Study outcomes
The study by Neuzil et al in 2020[47], tried to characterize health differences among Tennessee (United States) children treated for renal cancers that included Wilms tumor, renal cell carcinoma, and sarcoma	In TCR, for both race groups (black and white), Wilms tumor represented 80% of recorded malignancies. However, in the subgroup analysis of Wilms tumor cases, there was an over-representation of black children (n = 33, 26%) in relation to the state census for this specific race (16.8%). Compared to other renal malignancies, Wilms tumor exhibited the youngest median age at presentation (36 months/IQR: 12.0-48.0). Regarding overall survival, there was no significant difference between black and white patients with Wilms tumor	Wilms tumor remained the most common cancer of the kidney, and renal cell carcinoma was the least common. When combining all renal malignancies, specifically renal cell carcinoma and sarcoma, black children in the state of Tennessee presented with more advanced disease and experienced worse survival
The authors used the TCR (between 2004 and 2015) for patients aged 18 years or younger diagnosed with any form of renal malignancies (n = 160; Wilms tumor cases - 129, i.e., 81%). To further investigate treatment and outcomes, they conducted a retrospective cohort study of pediatric renal cancer patients from their Vanderbilt University Registry (ICR, n = 121; Wilms tumor cases - 100, i.e., 83%)	With reference to Wilms tumor, univariate logistic regression analysis for predicting mortality from pediatric renal malignancies showed a significant difference in case of renal cell carcinoma (OR = 5.75, 95%CI: 1.25-26.5, P value: 0.025) in TCR and (OR = 45.00, 95%CI: 3.77-536.92, P value: 0.003) in ICR, as well as for sarcoma (OR = 11.5, 95%CI: 4.00-33.07, P value < 0.001) in TCR. However, in multivariate analysis, only sarcoma showed a statistical significance (OR = 17.86, 95%CI: 4.68-68.2, P value < 0.001) in TCR	The survival disparities appeared to be reduced when treated at a comprehensive pediatric cancer center, which could alleviate the inequalities. Among both TCR and ICR, metastasis at diagnosis was independently predictive of worse prognosis
	Black patients were 26% of all patients in TCR (in ICR - 21%), presented more frequently with metastasis than white patients (37% vs 16%, P value: 0.021), and demonstrated worse overall survival (73% vs 89%, P value: 0.018). In ICR, similar survival among race groups (92% vs 93%, P value: 0.868) was recorded	The study highlighted the disparities in health outcomes due to socio-economic factors among pediatric renal cancer patients in the state of Tennessee
The study by Ekuk et al[48] in 2023 determined the one-year overall survival of Wilms tumor cases and their predictors among children diagnosed in the Pediatric Oncology and Surgical Units of MRRH, western Uganda	The one-year overall survival rate was found to be 59.3% (95%CI: 40.7-73.3)	Overall survival of Wilms tumor at MRRH was found to be 59.3%, and prognostic factors documented were unfavorable histology and tumor size greater than 15 cm
In this study, the treatment charts and files of children diagnosed and managed for Wilms tumor (n = 41) were retrospectively reviewed for the period from January 2017 to January 2021. The clinical details of children with histologically confirmed diagnoses were examined for demographic information, clinical and histological characteristics, and treatment modalities	Tumor size greater than 15 cm was identified as a significant predictor of poor survival, with a P value of 0.021. Tumor size above 15 cm was found to increase the risk of death from Wilms tumor by 6 times (95%CI: 1.32-34.95)
	Unfavorable Wilms tumor type (anaplasia) was another significant predictor of poor survival, with a P value of 0.012	The study highlighted the importance of tumor size and histology in predicting the survival outcomes for children with Wilms tumor
	Unfavorable histology type was found to increase the risk of death from Wilms tumor by 5.1 times (95%CI: 1.77-92.50)

TCR: Tennessee Cancer Registry; ICR: Institutional Cancer Registry; IQR: Interquartile range; OR: Odds ratio; CI: Confidence interval; MRRH: Mbarara Regional Referral Hospital.

In a study on different pediatric cancer cases in Poland, Zajac-Spychala and her colleagues followed 314 children and adolescents with newly diagnosed Wilms tumors over 72 months from January 2012 to December 2017[49]. They detected bacterial infections in 70 patients and 135 episodes of bacterial infections. The most common site of infection in their study was the gastrointestinal tract (51 episodes, 38%), followed by the urinary tract (42 episodes, 31%), and then the bloodstream infection (39 episodes, 29%). Furthermore, infections by Gram-positive bacteria, especially Clostridium and Staphylococcus species, were predominant (72 episodes, 53%), followed by Gram-negative bacteria such as Enterobacteriaceae and Pseudomonas (58 episodes, 43%). Interestingly, among patients with Wilms tumor, reports have shown the isolation of different atypical bacteria such as Leifsonia aquatica (L. aquatica), Streptococcus mitis (S. mitis), and Mycobacterium aurum (M. aurum)[50-52]. Of note, M. aurum is usually a non-pathogenic species, normally found in wet environments, and can rarely cause infection in immunocompromised patients. It is a fast-growing, acid-fast, Gram-positive bacterium. On the other hand, L. aquatica is a Gram-positive, rod-shaped, non-spore-forming aquatic bacterium that can cause infection in immunocompromised patients. Unlike both M. aurum and L. aquatica, S. mitis is an organism of our oral microbial flora. This Gram-positive coccus belongs to the viridans group Streptococci and can cause bacteremia in immunocompromised patients, cancer patients, and patients with neutropenia.

CONCLUSION

Globally, there are disparities in the management of Wilms tumor in regard to awareness, early diagnosis, and facility for appropriate treatment, which ultimately affect the overall prognosis. Generally, both a weakened immune system, as a consequence of neoplastic progression, and cancer treatment regimens are responsible for the susceptibility of patients to microbial infections. In the treatment of pediatric cancer patients, central venous catheter placement is important for the administration of chemotherapeutic agents. However, this route of drug administration is also associated with the risk of infectious complications. Therefore, careful monitoring and proper utilization of antimicrobial agents can only minimize the undesired morbidity.

On the other hand, the pathological processes of Wilms tumor are highly intricate. Its pathogenesis is linked to the deviation from the normal process of nephrogenesis. An appropriate understanding of these complicated pathways may unravel the enigma of other neoplasms, especially pediatric malignancies. Furthermore, the enhanced expression of WT1 in different adult cancers, which are primarily connected with lifestyle, is thought-provoking, besides the utilization of WT1 in immunotherapy. Overall, comprehensive knowledge of these matters is helpful in formulating effective therapeutic strategies.