A new study has reported that removing both ovaries before age 45 reduces risk of hormone receptor positive (ER+/PR+) breast cancer by approximately 40%. The study was designed to examine the association between surgical removal of ovaries before menopause and risk of breast cancer. Removal or impairment of ovaries may affect breast cancer risk by reducing cumulative exposure to ovarian hormones. The study included 4,490 breast cancer cases and 4,611 matched cancer-free controls aged 35 to 64 years in the Women's Contraceptive and Reproductive Experiences Study. The women provided information concerning history of ovariectomy, hysterectomy, and tubal sterilization during in-person interviews. Women who had not undergone any premenopausal reproductive surgery served as the comparison group for purposes of calculating risk of breast cancer.

Surgical removal of both ovaries before age 45 was found to be associated with an approximate 40% reduction in risk of breast cancer. The reduction in risk was limited to risk of estrogen and progesterone receptor positive (ER+/PR+) but not hormone receptor negative (ER-/PR-) tumors. Hysterectomy without removing the ovaries was found to reduce breast cancer risk by approximately 17% and hysterectomy with partial ovary removal reduced risk by 27%. No association with breast cancer risk was found for tubal ligation only or partial ovariectomy without hysterectomy. Women who were 45 or older at the time of surgery did not experience any risk reduction. The authors conclude that reproductive organ surgeries may affect breast cancer risk by altering ovarian hormone levels.