e15513 Background: Immune checkpoint inhibitor (ICI) therapy has made great achievements, but ICI monotherapies show less effectiveness in colorectal cancer patients. Biomarker exploration have carried out from PD-L1 expression, neo-antigen, gene mutation, etc., but no satisfactory results have been obtained. Methods: Patients, Colorectal cancer patients. Methods, Multi-color immunohistochemistry (multi-IHC) was used to evaluate CD8+ T cells, macrophages and natural killer cell (NK cell) in tumors and tumor stroma. The Shapiro-Wilk method was used to test the normality of the data, and the t-test or Mann-Whitney U test was used according to the test results. A two-sided P < 0.05 was considered a significant difference. Results: The study included 72 colorectal cancer patients, including 26 female (36.7%) and 46 male (63.8%), with a median age of 59.5 (50-67.3). There were 6 patients (8.3%) with BRAF mutation, 43 patients (59.7%) with KRAS mutation, and 56 patients (77.8%) with TP53 mutation. The results of immunohistochemistry showed that, BRAF mutation Vs BRAF wild-type or KRAS mutation Vs KRAS wild-type, the number or proportion of CD8+ T cells, macrophages or NK cells in tumor and tumor stroma were not statistically different. For TP53 mutation Vs TP53 wild-type, the number and proportion of CD8+ T cells or macrophages in tumor and tumor stroma were not statistically different. There was no statistical difference in the number and proportion of NK cells in tumor. But, the median number of NK cells in tumor stroma was 345 Vs 129, p = 0.06, and the proportion of NK cells was 5.2% Vs 1.39%, p = 0.02. Conclusions: There is no significant change in the immune microenvironment of colorectal cancer patients with BRAF mutation and KRAS mutation. There are more NK cells in tumor stroma of colorectal cancer patients with TP3 mutation.
