Evaluation of pancreatic adenocarcinoma with tumor budding and lymphocytic infiltration as prognostic marker

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent type of pancreatic neoplasm. It is a highly aggressive lethal malignancy related to its delayed in diagnosis and limited response to treatments. The incidence and mortality of pancreatic cancer have been increasing over the years. Tumor budding is a proven independent, adverse prognostic factor in PDAC. It is helpful for improvement of prognosis in PDAC in early and precise diagnostic modalities. Tumor budding should be conveyed in pathology reports and taken into account by future oncologic staging systems.

Key Words: Pancreatic ductal adenocarcinoma; Tumor-infiltrating lymphocytes; Tumor Budding; Prognostic marker; Evaluation

Core Tip: Pancreatic ductal adenocarcinoma is highly invasive pancreatic neoplasm, having globally 495773 new cases and 466003 new deaths reported in 2020. This article is to evaluate the prognostic importance of tumor budding (TB) and tumor-infiltrating lymphocytes in pancreatic ductal adenocarcinoma and its correlation as prognostic marker. A high TB was a poor prognostic feature and might be a target for tumor-specific treatments. While high T-cell infiltration, especially of CD8+ T cells is linked to better outcomes. Future, TB and tumor lymphocytic infiltration should be taken into consideration and included in pathology reports. This knowledge is crucial for clinicians to better assess patient prognosis.

TO THE EDITOR

Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent pancreatic carcinoma, with an overall 5-year survival of 8%[1]. PDAC is the seventh-highest cause of cancer deaths in the world, it ranks in the top four in developed countries[2]. PDAC is a highly aggressive tumor and is usually locally advanced and/or metastatic at the time of diagnosis. Therefore, many times it is difficult to perform surgical resections. At the International Tumor Budding Consensus Conference (ITBCC) for colorectal carcinoma, a scoring system was established for tumor budding (TB)[3]. There is new evidence concerning the aggressive PDAC growth and pathogenesis over the past years related to its basic histomorphological features to advance molecular studies. The evaluation of TB and tumor-infiltrating lymphocytes (TILs) has gains great importance, because it can help the relationship between drug resistance, which is effective in the poor prognosis of pancreatic cancers and tumor phenotype. Recently an article, evaluation of TB, desmoplastic reaction, and lymphocytic infiltration in predicting survival for PDAC observed role of desmoplastic reaction at tumor and given new insight[4]. However, most critical hindrance for TB reporting is the absence of a standard determination method related to the use of different cutoff values and groupings in the analysis of TB that limits the ability to draw conclusions. Therefore, more studies should be performed to improve the reproducibility of TB evaluation.

Current situation and challenges of PDAC

PDAC is an invasive pancreatic epithelial neoplasm with glandular (ductal) differentiation. The incidence and mortality of pancreatic cancer have been increasing over the years[5]. PDAC on histopathology is characterized by infiltrating well to poorly formed glandular/ductal structures surrounded by remarkably desmoplastic stroma, frequent lymphovascular and perineural invasion, necrosis, and thrombosis. Many histopathological features that are effective in the prognosis are known like tumor differentiation, perineural, and lymphovascular invasion, regional lymph node metastasis, surgical margin positivity, etc. However, TB and TILs are not written in pathology reports. TB and TILs should be conveyed in pathology reports and taken into consideration in future oncologic staging systems with standard determination method.

Approaches with tumor buds as a prognostic marker in PDAC

In PDAC, it is observed in many studies that microenvironment play important role to facilitate tumor growth, encourage metastasis, and include a physical barrier to treatment administration. TB is biologically correlated to the induction of epithelial-mesenchymal transitions and tumor progression. TB is a type of invasive growth pattern observed on the microscopic histopathological examination at immediate tumor front. It appears as isolated tumor cells or as a small non-glandular tumor cell cluster and is generally believed to represent the epithelial-mesenchymal transition of the tumors[6]. TB is defined as a single tumor cell or a cluster of up to four tumor cells in the stroma at the outer edge of the tumor. TB in the densest budding area at × 20 magnification (one hot-spot, 0.785 mm²). It is graded based on the ITBCC categories of TB into low grade as 1 or 2 and high grade as 3. The number of tumor buds were counted and reported as low (0-9 buds) and high (≥ 10 buds) grades per 0.785 mm² hotspot. In a variety of solid tumors, TB grading is now recognized as an important prognostic marker. Recently, the relationship between TB and podoplanin expression in tumor cells has been examined in oral squamous cell carcinoma[7]. TB in histopathological findings are done according to the ITBCC grading guidelines. The ITBCC recommends recommend concrete steps for standardization using a 0.785 mm² area (using a 20 × objective with a 20 mm eyepiece) for TB evaluation, and the “hotspot” method, which involves scanning 10 fields (10 × objective) along the invasive front and counting TB in the highest density area (20 × objective). ITBCC scoring can be easily applied in the evaluation of TB in operated PDACs. Peritumoral and intratumoral budding were assessed according to it.

TB is associated with epithelial-mesenchymal transition and diminished survival. In high grade TB of PDAC cases showed reduced anti-tumor immunity. In addition, high TB is a poor prognostic feature as well as being associated with lymph nodal metastasis, lymphovascular/perineuronal invasion and poor differentiation, suggesting that it can be a predictive finding for the locally invasive cancer[8]. Lugli et al[3] observed TB is found to be associated with distant metastasis. The evaluation of TB has gains great importance, because it can help the relationship between drug resistance, which is effective in the poor prognosis of pancreatic cancers and tumor phenotype, it is observed that significantly shorter overall survival is seen in PDAC patients with high-grade TB. TB is a proven independent, adverse prognostic factor in PDAC.

Approaches with TILs as a prognostic marker in PDAC

Pancreatic cancer is often marked by an immunologically “cold” milieu, as desmoplastic stroma restricts T cell penetration. TILs evaluation may be a valid, less expensive, and readily available method on microscopic examination. The investigation of the tumor microenvironment (TME) has highlighted the significance of TILs in prognostic assessment of PDAC. The level of TILs was assessed as absent, low, moderate, or high and scored as 0, 1, 2, and 3, respectively[9]. The presence of CD8+ T cells, which are key players in the immune system’s ability to eliminate tumor cells, is a positive prognostic factor. The absence of cytotoxic CD8+ T cell infiltration is one of the PDAC’s TME most distinctive characteristics. T helper 17, T helper 22, CD4+, and gammadelta T cells are among the other T cell subsets in the TME that have been observed to exhibit pro-tumorigenic functions.

The most accurate indicator of how well immune checkpoint inhibitor therapy will work is the presence of cytotoxic CD8+ T cell infiltration in tumors. Subsets of TILs, particularly CD3+, CD8+, and FoxP3+ T cells, are highly correlated with long-term oncological outcomes in patients with PDAC, according to a comprehensive review and meta-analysis on the predictive usefulness of TILs in pancreatic cancer by Orhan et al[10]. It shows that high TILs alone are insufficient without specifying functional subsets and microenvironmental interactions. Better results are correlated with more infiltration of T cells, especially CD8+ T cells. TILs are associated with survival in determining the prognosis in pancreatic cancer[10].

Also noted that high grade TB cases exhibit notably reduced densities of stromal and intratumoral T cells. The primary purpose of CD8+ T cell priming is to serve as a corroboration mechanism between CD4+ T cells in adoptive immunity and innate immunity cells, such as dendritic cells and natural killer cells. In pancreatic cancer settings, Xiang et al[11] showed that elevated neutrophil-lymphocyte ratio was linked to worse and reduced CD8+/CD28- and CD4+/CD25+ cell subsets. Farhood et al[12] observed that a tumor that is immunogenically warm and responds well to immunotherapy is characterized by high TILs, particularly CD8+ lymphocytes, and the makeup of the TME, both of which predict prognosis. CD8+ cells can be considered as an independent prognostic factor for survival improvement in patients[13]. The type of lymphocytes and number of lymphocytes within the TME can significantly influence the tumor’s growth, survival, and response to treatment. Increased knowledge of the stage and histological characteristics of PDAC has led to the prominence of tailored therapies for particular subgroups. New targeted treatments have been developed as a result of understanding the role lymphocytes play in pancreatic cancer.

Other tumor biomarkers for PDAC

In a comprehensive review of Ballehaninna and Chamberlain[14] from United Kingdom observed that various tumor biomarkers for PDAC are carcinoembryonic antigen, carbohydrate antigen 125, carbohydrate antigen 242, and carbohydrate antigen 50. However, none of these markers of carbohydrate antigen, showed indicators for diagnostic potential. In the terms of diagnostic, prognostic, recurrence, and surveillance capabilities, serum carbohydrate antigen 19-9 is the most extensively studied and validated biomarker for pancreatic cancer[14]. Carbohydrate antigen 19-9 primarily serves as a diagnostic tool, while TB and TILs are more strongly linked to prognosis.

Although circulating tumor DNA has emerged as a promising biomarker in a variety of malignancies, including thyroid, lung, and colorectal cancers, it has not yet become part of routine clinical practice in PDAC. Recently, multi-omics studies like genomic and proteomic analyses in the primary PDAC tumor have revealed subclones with different metastatic potentials by driving biological processes in tumor spread[15]. This new biomarkers are consider to help in its context within which it exists. The circulating tumor DNA have challenges in sensitivity, especially for early-stage pancreatic tumors, and tumor heterogeneity can affect accuracy. While multi-omics studies genomics, transcriptomics, proteomics, etc. is complex, requiring advanced bioinformatics and are often expensive. With limited prognostic biomarkers, the effective treatment and outcome prediction in pancreatic cancer remain a challenge. In surgically non resectable patients, multiagent chemotherapy regimens are usually used in PDAC patients. Further invention and validation studies are needed to identify strong biomarkers.

CONCLUSION

PDAC is a highly aggressive tumor with very limited treatment options and few prognostic biomarkers. Early and precise diagnostic modalities could have a major impact on the improvement of the prognosis of PDAC. TB and lymphocytic infiltration are both important prognostic factors in PDAC. High-grade TB is associated with overall poorer survival, while high T-cell infiltration, especially of CD8+ T cells, is linked to better outcomes. Clinicians need to know this information in order to evaluate patients’ prognoses more accurately and adjust treatment plans appropriately. Future, TB and tumor lymphocytic infiltration should be taken into consideration and included in pathology reports. This knowledge is crucial for clinicians to better assess patient.