DNMT1 and breast cancer: Sowinska [4] demonstrated that combined DNMT1 and DNMT3b siRNAs could enhance promoter demethylation and re-expression of CXCL12 in MCF-7 breast cancer as well as AsPC1 in pancreatic carcinoma cell lines, and suggested that they acted synergistically in inhibiting CpG island hypermethylation of tumor suppressor genes.