PKD1 and cancer: 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.