ESR1 and breast cancer: Interestingly, among the group of genes strongly induced by PIAS1 knockdown, several genes are known to be clinically relevant to breast cancer, including breast cancer DNA methylation signature genes Cyclin D2 (CCND2) and Estrogen receptor (ESR1), candidate tumor suppressor WNT5A, progestagen-associated endometrial protein (PAEP), as well as leucine zipper, downregulated in cancer 1 (LDOC1).