ESR1 and ovarian cancer: We initiated the studies on the human ovarian cancer cell lines, SKOV3 and A2780cis, by determining their expression of ERα and ERβ, respectively, and by exploring the effect of the non-subtype-selective, natural hormone E2, which binds to ERα and ERβ with similar affinity, and the two subtype-selective agonists KB9520 (ERβ-selective) and PPT (ERα-selective), on the growth of these cells (Fig. 1).