SMAD4 and gastric cancer: Therefore, we tested whether differences existed between younger and older age groups, in background mutation densities of whole cancer exomes and/or frequencies of 25 driver gene mutations (TP53, CDH1, SMAD4, PIK3CA, RHOA, ARID1A, KRAS, MUC6, APC, BCOR, EYA4, BNC2, RNF43, ABCA10, CTNNB1, MACF1, SMAD2, SOHLH2, RASA1, FAM46D, PLB1, CNGA4, AGO4, ERBB2, PTPRC, which were reported as significantly mutated genes in non-hypermutated gastric cancers in the TCGA study).