[Clinical and pathological characteristics and prognostic analysis of colorectal cancer associated with breast cancer susceptibility gene mutations].

Objective: To investigate the mutation status of breast cancer susceptibility genes (BRCA) in colorectal cancer and the relationship between BRCA and the clinical-pathological characteristics and prognosis of colorectal cancer. Methods: A total of 132 colorectal cancer tissue specimens surgically resected at Shanxi Cancer Hospital from 2018 to 2021 were collected. Second-generation sequencing was used to detect BRCA mutations. Immunohistochemical staining assessed the infiltration density of CD3+, CD4+, and CD8+ T cells, and CD20+ B cells. The association between BRCA mutations and clinical-pathological features, immune cell infiltration density, and prognosis of colorectal cancer was analyzed. Results: Among 132 colorectal cancer cases, the overall BRCA mutation rate was 9.09% (12/132), with BRCA1 mutation rate at 3.03% (4/132) and BRCA2 mutation rate at 6.06% (8/132). Compared with the BRCA wild-type group, the BRCA mutation group exhibited smaller tumors (P=0.036), less vascular or nerve invasion (P=0.041), and lower tumor budding grades (P=0.013). Tumor microenvironment analysis revealed that the infiltration densities of CD3+, CD4+, and CD8+ T cells in the BRCA mutation group were 1 729.66 (652.91, 3 065.98)/mm², 438.36 (97.37, 718.43)/mm², and 1 017.86 (506.19, 2 257.35)/mm², respectively, all higher than those in the BRCA wild-type group [555.72 (304.58, 933.26)/mm², 89.34 (58.15, 178.35)/mm², and 354.23 (157.78, 752.37)/mm², respectively, all P＜0.05]. Molecular feature analysis revealed five cases of TMB-H in the BRCA-mutant group and three cases in the BRCA-wild group, with a statistically significant difference between the two groups (P＜0.001). Survival analysis revealed no association between BRCA mutation status and overall survival in colorectal cancer patients (P＞0.05). Multivariate Cox regression analysis identified clinical stage as an independent predictor of overall survival, with patients at stages Ⅲ-Ⅳ exhibiting poorer prognosis (HR=5.359, 95% CI: 1.124-25.546). Conclusion: BRCA-mutated colorectal tumors exhibit lower invasiveness, higher TMB-H rates, and abundant immune cell infiltration in the tumor microenvironment, suggesting that patients with BRCA-mutated colorectal cancer are more likely to benefit from immunotherapy.