MCF7 is a human breast adenocarcinoma cell line positive for estrogen receptor alpha, and MDA-MB-231 is a human breast carcinoma cell line negative for estrogen and progesterone receptors as well as HER2. The IGFBP3 promoter displays hypermethylation, and there is reduced IGFBP3 expression in MCF7, while in MDA-MB-231, the promoter is relatively hypomethylated, and IGFBP3 is over-expressed compared to HMEC. The gene discussed is ESR1; the disease is breast carcinoma.