ESR1 and ovarian carcinoma: Cell line ZR-75/1 is known to be highly estrogen and progesterone dependent [36] and was found to have the highest c-erbB2-expression among eight characterized breast- and four ovarian-cancer cell lines [37], whereas MDA-MB231 cells are ER- and PR-receptor negative and express HER-2/neu only at very low levels [38].