Whole-exome sequencing revealed several candidate mutations in GC peritoneal carcinomatosis: mutations in druggable genes (TEP1, PRKCD, BRAF, ERBB4, PIK3CA, HDAC9, FYN, FASN, BIRC2, FLT3, ROCK1, CD22, and PIK3C2B) and mutations in metastasis-associated genes (PTPN13, TNFSF12, L1CAM, DIAPH3, ROCK1, TGFBR1, MYO9B, NR4A1, and RHOA). This evidence concerns the gene HDAC9 and gastric cancer.