Clinicopathological, Immunohistochemical, and PMS2 Gene Expression Profiling of Patients with Sporadic Colorectal Cancer

Background: The DNA mismatch repair (MMR) system is one of the molecular pathways involved in colorectal cancer (CRC) carcinogenesis that consists of several genes, including MLH1 (MutL homolog 1), MSH6 (MutS homolog 6), MSH2 (MutS homolog 2), and MSH3 (MutS homolog 3). The protein encoded by PMS2 (post-meiotic segregation 2) is also essential for MMR. Here, we address the correlation between immunohistochemical and transcriptional expression of PMS2 with the tumor grade and clinical stage of non-hereditary/sporadic CRC disease. Methods: This study retrospectively analyzed 67 colorectal resections performed for 38 male and 29 female patients. Random biopsies were taken by a gastroenterologist from patients referring to three hospitals in the cities of Zanjan, Urmia and Qazvin (Iran) during 2017-2019. All specimens were examined and classified for localization of tumor, pathological stage and grade. The PMS2 protein expression was studied immunohistochemically and analysis of mRNA expression was performed in the same tissue sections. Results: Immunohistochemistry and quantitative real-time polymerase chain reaction (PCR) analysis showed a decrease in PMS2 expression compared with paracancerous tissue ( P <0.001), which correlated with tumor stage. In addition, reduced PMS2 expression was correlated with the tumor differentiation grade, underlining a connection between downregulation of PMS2 and progression of CRC. Comparing the PMS2 mRNA levels in different groups showed the following results: 0.92 ± 0.18 in patients with Stage I CRC tumor, 0.86 ± 0.38 in Stage Ⅱ, 0.50 ± 0.29 in Stage Ⅲ, and 0.47 ± 0.23 in Stage Ⅳ. Conclusion: These findings suggest that PMS2 may provide a potential reliable biomarker for CRC classification by combined immunohistochemical and mRNA analysis.