ESR1 and breast cancer: In some studies, ERα-expressing CAFs have been reported to promote prostate and endometrial cancer cell proliferation [32, 36]; in other studies, CAFs attenuated prostate tumor cell invasiveness and immune cell infiltration by altering the levels of anti-angiogenic factors, ECM remodeling factors as well as chemokines, in addition to conserving chemosensitivity in certain breast cancer cell lines [37–39].