STK11 and breast cancer: Estrogen is reported to regulate LKB1 gene expression through transcriptional regulation, and ERα binding site is found in the promoter region of LKB1. In MCF-7 breast cancer cells, 17β-estradiol can downregulate both mRNA and protein level of LKB1 through inhibiting LKB1 promoter activity by reducing the binding of ERα to the promoter of LKB1 [65].