ESR1 and cancer: These included two estrogen-receptor-positive (ER+) and progesterone-receptor-positive (PR+) lines (T-47D and MCF-7), one ER+ (SK-BR-3), and four triple-negative (TN) cancers that lacked the estrogen, progesterone, and Her2/neu receptors (BT-549, Hs578T, MDA-MB-231, and MDA-MB-468).