PGR and breast cancer: In the Women’s Contraceptive and Reproductive Experiences case-control study, bilateral oophorectomy was associated with stronger reductions in the incidence of estrogen receptor (ER)+/progesterone receptor (PR)+ breast cancers (OR = 0.55; 95% CI: 0.45, 0.68) compared to ER-/PR- tumors (OR = 0.82; 95% CI: 0.63, 1.07) [40].