The Impact of PD-1 Inhibitor Combined with Bevacizumab on Tumor Immune Cells in MSS/pMMR Advanced Colorectal Cancer Patients with Failed First-Line Treatment

Objective: To investigate the effects of PD-1 inhibitor combined with bevacizumab monoclonal antibody on tumor immune cells in patients with first-line treatment failure in MSS/pMMR advanced colorectal cancer. Methods: A total of 40 patients with advanced colorectal cancer who failed first-line treatment were selected using a random number table method from Qinghai University Affiliated Hospital from October 2021 to June 2023. Ten patients in the control group were treated with FOLFIRI combined with bevacizumab. The experimental group of 30 patients was treated with sintilimab combined with bevacizumab, and the post-treatment effects of the two groups of patients were compared. The expression levels of CD8+ T cells, tumor-associated macrophages, and tumor-associated fibroblasts were evaluated comprehensively to assess the effects of sintilimab combined with bevacizumab on patients with first-line treatment failure in MSS/pMMR advanced colorectal cancer. Results: There was no statistically significant difference in the positive expression rates of CD8+ T lymphocytes, TAMs, and CAFs before and after treatment in both groups (P>0.05). There was no statistically significant difference in the comparison of the therapeutic effects of two groups of tumors (P>0.05), but the experimental group had higher PFS, mPFS, ORR, and DCR than the control group. There was no statistically significant difference in the occurrence rate of drug-related adverse reactions after treatment between the two groups (P>0.05). Conclusion: By using the combination of sintilimab and bevacizumab in the first-line treatment of MSS/pMMR advanced colorectal cancer patients who failed first-line treatment, not only can the tumor immune microenvironment of patients be improved, but it can also transform the cold tumor immune suppression state into a hot tumor immune supportive state. While ensuring the safety of drug adverse reactions, it enhances the patients' anti-tumor ability and clinical treatment effects, further increasing the clinical application value.