Taken together, these results unequivocally show that RNF43-G659Vfs*41 mutation in colon, endometrial and stomach cancers primarily occurred in tumors with low MLH1 expression and presumably defective DNA mismatch repair, suggesting that the seven G repeat (bp1969-1976) of RNF43 coding sequence is highly prone to single bp deletion in the absence of proficient DNA repair. This evidence concerns the gene RNF43 and gastric cancer.