We determined whether the expression levels of five antiapoptotic genes were different in ER-positive and ER-negative cell lines by examining two normal breast epithelial cell lines (HMEC2.6 and HME1), four ER-positive breast cancer cell lines (MCF-7, T47D, BT474, and ZR-751), and four ER-negative cell lines (SKBR3, MDAMB-453, BT549, and HCC70). The gene discussed is ESR1; the disease is breast cancer.