Survival benefits of immunotherapy combined with chemoradiotherapy in metastatic colorectal cancer: an analysis based on data from the SEER database.

OBJECTIVES

Chemoradiotherapy (CRT) alone shows limited efficacy in improving outcomes for metastatic colorectal cancer (mCRC) patients. This study aimed to comprehensively evaluate the survival benefits of combining CRT with immunotherapy (CRT + IMT) in this population.

METHODS

Data from the SEER database were extracted for mCRC patients diagnosed between 2010-2015 and 2018-2020. Survival outcomes were assessed using Kaplan-Meier analysis, log-rank test, Cox regression, and propensity score matching (PSM) to minimize baseline differences between treatment groups, and multivariable Cox models were constructed based on variables selected by LASSO regression.

RESULTS

A total of 2,451 patients were identified, with 1,888 receiving CRT alone and 563 CRT + IMT. After 1:2 PSM, 1,594 remained. Kaplan-Meier curves showed CRT + IMT significantly improved overall survival (OS, p<0.0001) and cancer-specific survival (CSS, p<0.0001). Multivariable Cox confirmed CRT + IMT as an independent predictor (OS HR=0.54, 95 % CI: 0.44-0.65; CSS HR=0.54, 95 % CI: 0.44-0.66). Favorable factors included distal colon/rectal tumors, surgery, and combined therapy, while older age (>60), advanced stage, N2, and metastasis predicted worse survival. The subgroup analyses revealed a more pronounced benefit in specific cohorts, and significant interactions were observed for factors such as histologic grade and nodal stage.

CONCLUSIONS

The combination of CRT and immunotherapy confers a significant survival advantage over CRT alone in patients with mCRC, supporting its potential role in optimized treatment strategies.