Prognostic Value and Immunohistochemical Analysis of Mismatch Repair Deficiency in Patients with Stage II and III Colorectal Carcinoma—A Single-Center Study

Background and objectives: Deficient mismatch repair (MMR) status is associated with good prognosis but poor therapeutic response to adjuvant chemotherapy in patients with colorectal cancer. However, there are some opposed arguments considering therapeutic outcomes in patients with evidenced MMR deficiency in colorectal cancer. The aim of the study was the investigation of prognostic value and immunohistochemical analysis of the MMR-deficiency tumors. Materials and Methods: The study enrolled 104 patients with resected stage II and III colorectal cancer samples from the period 2018–2019. Results: The tumors with deficient MMR status were significantly associated with age up to 50 years and right-sided localization (p < 0.001). During the follow-up period of 22.43 ± 6.66 months, 21 patients (20.2%) died, whereas 14 patients (13.5%) had relapses. The loss of mutL homologue 1/postmeiotic segregation increased 2 (MLH1/PMS2) expression, compared to proficient MMR tumors, was associated with shorter disease-free survival in patients with lymphovascular invasion (p < 0.05), perineural invasion (p < 0.01), stage III (p < 0.05) and high-grade tumor (p < 0.05). Conclusions: This retrospective pilot study of a single-center cohort of patients with stage II and III colorectal cancer highlights the clinical importance of using immunohistochemistry (IHC) analysis as a guide for diagnostic algorithm in a country with limited resources, but with a high prevalence of colorectal carcinoma in the young patients. MMR-deficiency tumors compared with proficient MMR colorectal cancer was not shown to be a significant predictor of disease-free and overall survival.