ESR1 and ovarian cancer: For example, tumor-extrinsic ERα is implicated in enhancing the immunosuppressive activity of myeloid-derived suppressor cells (MDSC) during ovarian cancer progression.3 In support of a tumor-extrinsic antitumor activity of ERβ, syngeneic murine melanoma cells grafted to recipient ERβ knockout (KO) animals grew more robustly than those in wild-type (WT) recipient mice.4 More recent studies implicate ERβ in promotion of antitumor immunity.5 6 However, how tumor-extrinsic activity of ERβ is regulated in an ER subtype-specific manner remains unclear.