MUC4 , MUC16 , and TTN genes mutation correlated with prognosis, and predicted tumor mutation burden and immunotherapy efficacy in gastric cancer and pan‐cancer

Abstract

Dear Editor, Previous studies reported that MUC16 mutation was associated with better prognosis and higher tumor mutation burden (TMB) in gastric cancer, while TTN mutation was associated with better response to immune checkpoint blockage in solid tumors, but the potential mechanisms were still unclear. 1,2 Through the analysis in TCGA gastric adenocarcinoma cohort (N = 443) and FUSCC gastric cancer cohort (N = 177), we identified two mucin genes, MUC4 and MUC16. These two mucin genes were selected based on mutational frequencies in gastric cancer, gene length, correlation with prognosis, and previous studies (Table S1, Figure S1). We further included the longest gene, TTN, into analysis, in consideration of its high mutation frequency and close correlation with TMB. We observed high potency MUC4, MUC16, and TTN had in predicting TMB in both TCGA and FUSCC cohort. MUC4-, MUC16-, and TTN-mutated cancer showed higher TMB (Figure 1). Mutation numbers of MUC4, MUC16, and TTN were closely correlated with TMB (Table S2). In TCGA cohort, correlation coefficient reached the highest of 0.782 when combined mutation numbers of three genes together; while in FUSCC cohort, the correlation coefficient reached the highest of 0.748 for MUC16 plus TTN, and was 0.735 for three genes. The receiver operating characteristic (ROC) curve further proved the efficacy using mutation numbers to predict TMB (Figure 1, TMB high was defined as top 20% in each cohort, TCGA: >20 muta-tions/Mb, FUSCC: >8 mutations/Mb). In TCGA cohort, area under ROC curve (AUROC) reached the highest of 0.936 when combined three genes together; while in FUSCC cohort, AUROC reached the highest of 0.925 for MUC16 plus TTN, and was 0.915 for three genes together. The Youden index is shown in Tables S3 and S4. In both TCGA and FUSCC cohort, high TMB was correlated with better overall survival (OS) (Figure 1). High mutation number of MUC4, MUC16, and TTN was correlated with bet-This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ter OS in TCGA cohort, while showing a trend of better OS in FUSCC cohort (Figure 1, high mutation number was defined as top 20% in each cohort). In order to realize whether mutation of MUC4, MUC16, and TTN gained functional change or just contributed to TMB, we further analyzed the gene mutation sites distribution (Figure S2). 3,4 Somatic mutations of MUC16 and TTN were sporadic in both TCGA and FUSCC cohort. Only MUC4 gene had a slightly high mutation rate of H4205Q in TCGA cohort (2.04%) and V3305_S3320del in FUSCC cohort (7.34%). The univariate and multivariate survival analysis showed H4205Q mutation was independently correlated with worse OS in TCGA cohort (Table S5, HR (95% CI): 2.266 (1.028-4.994), P = .043), while V3305_S3320del was independently correlated with better OS in FUSCC cohort (Table S6, HR (95% CI): 0.221 (0.053-0.928), P = .039). Of note, TMB and mutation numbers were not independent prognostic factors, which indicated them as marker for prognosis but not determining factors. We further clarified the potential mechanism why MUC4 and MUC16 mutation, high TMB and high mutation numbers were correlated with prognosis. In both TCGA and FUSCC cohort, patients with MUC4 mutation showed lower T stage, while MUC16-mutated patients showed lower N stage. High TMB and high mutation numbers were correlated with lower N stage in TCGA cohort but lower T stage in FUSCC cohort (Table S7, P