For example in androgen-independent prostate cancer and pancreatic cancer PKD1 expression is downregulated.22–24 In breast cancer and gastric cancer PKD1 expression is down-regulated through promoter hypermethylation.25,26 In contrast, PKD2 and PKD3 exert cancer promoting properties, since they are necessary for the regulation of genes and proteins involved in metastasis and invasion. This evidence concerns the gene PKD1 and gastric cancer.