Can an oopherectomy reduce breast cancer recurrence in premenopausal women?

Quite possibly: Removing the ovaries dramatically decreases your estrogen production. Any estrogen responsive or estrogen receptor positive cancers will lose that stimulation, and decrease the chance of developing that type of cancer. Recurrence risk of estrogen receptor positive cancers will decline.

Yes: But that's a pretty extreme step. Basically, any reduction in estrogen can reduce risk. Pregnancy suppresses estrogen production, which is why nulliparity (not having babies) raises the risk. Nuns have higher brca risk! so while oophorectomy will reduce risk, it is also possible to reduce risk with medications. Raloxifene is drug which works very well with few side effects. See your doctor!

YES for ER positive: Oopherectomy has been proven to reduce recurrence in estrogen-receptor positive pre-menopausal women. Prior to tamoxifen, it was a commonly used treatment for metastatic disease and is now known to reduce recurrence in high-risk premenopausal hormone-receptor positive breast cancer, even without the use of other endocrine therapies.