Prognostic value of CD8+ TILs and MMR status and their correlation with clinical outcomes in rectal cancer

Abstract Objective To explore the relationship between CD8 + tumor-infiltrating lymphocytes (TILs) in rectal cancer, mismatch repair (MMR) status, and patient prognosis. Methods A total of 414 paraffin-embedded tissue samples from patients with pathologically confirmed stage Ⅰ–Ⅲ rectal cancer were included in this study. Tissue microarrays (TMAs) with a thickness of 4 µm were prepared, and immunohistochemical staining was performed using a CD8 antibody to detect the expression of CD8-positive cells. MMR status was assessed using immunohistochemical markers (MSH2, MSH6, MLH1, PMS2). Results CD8 + TILs were expressed on T lymphocytes. Density was significantly associated with tumor invasion depth, lymph node metastasis, and MMR status (P < 0.05), but not with age, sex, surgery type, or tumor size (P > 0.05). Patients with high CD8 + TIL density and stable MMR status had longer overall and progression-free survival. Univariate and multivariate Cox analyses indicated low CD8 + TIL density and unstable MMR status as independent risk factors for poor prognosis. Conclusion CD8 + TIL density and MMR status may serve as combined prognostic biomarkers in rectal cancer, with higher density and stable MMR status linked to better outcomes and potential guidance for immunotherapy strategies.