Prognostic value of peripheral inflammatory markers in pMMR colorectal cancer patients receiving immunotherapy

The clinical benefit of immunotherapy in proficient mismatch repair (pMMR) colorectal cancer (CRC) remains limited and heterogeneous. Identifying reliable and easily accessible biomarkers for prognostic stratification is urgently needed. Systemic inflammatory markers can reflect tumor–immune interactions. This retrospective study included 97 patients with pMMR colorectal cancer who received immunotherapy at our institution. Peripheral inflammatory markers, including the neutrophil-to-lymphocyte ratio (NLR), cancer–inflammation prognostic index (CIPI), and systemic immune–inflammation index (SII), were evaluated. Overall survival (OS) was analyzed using the Cox proportional hazards model. A prognostic nomogram was constructed based on variables selected according to univariate significance and clinical relevance to estimate 1-year and 3-year OS. Model performance was assessed using the concordance index (C-index), and calibration of the 1-year OS prediction was evaluated using bootstrap resampling. Risk stratification was further evaluated using Kaplan–Meier analysis. Univariate analysis showed that NLR, CIPI, carcinoembryonic antigen (CEA), and targeted treatment were associated with OS. Among the 26 patients who received targeted therapy, 14 received anti-EGFR agents, 7 received anti-VEGF agents, and 5 received tyrosine kinase inhibitors (TKIs). These treatments were analyzed together as a single variable in the survival analysis because of the limited sample size. In multivariate analysis, targeted treatment remained the only independent prognostic factor (HR = 2.48, P = 0.023), while NLR showed a borderline association with worse survival (HR = 2.14, P = 0.061). A nomogram incorporating these clinically relevant variables showed acceptable discrimination (C-index = 0.732), and the 1-year calibration curve demonstrated reasonable agreement between predicted and observed survival probabilities. Patients in the high-risk group had significantly poorer OS than those in the low-risk group ( P = 0.011). Peripheral inflammatory markers, particularly NLR and CIPI, may provide supplementary prognostic information for patients with pMMR colorectal cancer receiving immunotherapy. The proposed nomogram may serve as a preliminary tool for risk stratification, although further prospective validation is needed.