Mutations of METTL3 predict response to neoadjuvant chemotherapy in muscle-invasive bladder cancer

Neoadjuvant chemotherapy (NAC) followed by radical cystectomy is the current gold standard treatment for muscle-invasive urothelial bladder cancer (MIBC). Nonetheless, some MIBC patients showed limited pathological response after NAC. Herein, we used whole-exome sequencing (WES) to identify genetic mutations in MIBC that can predict NAC response.

The somatic mutation of METTL3 can be a potential predictive biomarker of NAC response in MIBC patients. Relevance for patients: MIBC patients bearing mutated METTL3 display a pathological response to NAC and have a significantly longer overall survival or disease/progression-free survival as compared to the patients bearing wild-type METTL3. Thus, the somatic mutation of METTL3 is a potential biomarker for predicting response to NAC in MIBC patients, assisting doctors in making the clinical decision.

Forty MIBC patients were enrolled in this study, in which 33 were successfully examined by WES and Sanger sequencing in the discovery cohort (n=13) and the validation cohort (n=20), respectively. ANNOVAR software was used to identify the potential mutations based on the data of WES. In addition, tumor-specific somatic mutations including single nucleotide variants and indels were called with the muTECT and Strelka software. The mutational analysis of specific genes was carried out based on the data from cBioPortal for Cancer Genomics.

In the discovery cohort, the mutation frequencies of TP53, MED16, DRC7, CEND1, ATAD5, SETD8, and PIK3CA were significantly higher in 13 MIBC patients. Specifically, the presence of somatic mutations of APC, ATM, CDH9, CTNNB1, METTL3, NBEAL1, PTPRH, RNASEL, and FBXW7 in NAC responder signifies that these mutations were potential predictors of pathological response to NAC. Furthermore, somatic mutations of CCDC141, PIK3CA, CHD5, GPR149, MUC20, TSC1, and USP54 were exclusively identified in NAC nonresponders, suggesting that these mutations may participate in the process of NAC resistance. In the validation cohort, the somatic mutations of CDH9, METTL3, and PTPRH were significantly enriched in NAC responders while the somatic mutation of CCDC141 was significantly enriched in NAC nonresponders. Furthermore, survival analysis revealed that the patients expressing mutated METTL3 have a longer overall survival and disease- or progression-free survival than the patients acquiring wild-type METTL3.