Breast cancer patients who take estrogen-lowering drugs may avoid having to undergo mastectomy, according to a study to be presented at the Annual Meeting of the American Society of Clinical Oncology.

The study involved 352 postmenopausal women with estrogen-receptor positive (ER+) breast tumors who received estrogen-lowering therapy for 16 weeks before surgery for breast cancer. Researchers monitored the extent of their tumors before and after the drug treatment.

All women in the study had stage II or III breast cancer and were assigned to groups based on the surgical option that was most appropriate for them: marginal, mastectomy-only, or inoperable. The women were randomly assigned to receive one of three estrogen-lowering agents: exemestane, letrozole, or anastrozole.

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Researchers reported that the treatment shrank the tumors in many of the women and improved surgical outcomes . Specifically, 82% of women in the marginal group, 51% in the mastectomy-only group, and 75% in the inoperable group had successfully breast-conservation surgery instead of mastectomy.

“ER+ breast cancer can be thought of as a chronic disease because patients generally take estrogen-lowering agents for many years after surgery to repress recurrence,” said Matthew Ellis, MD, PhD, the study’s chair. “In other chronic diseases, such as hypertension or diabetes, a patient’s response to treatment is continually monitored. But we’ve never done that with breast cancer. By treating breast cancer patients with estrogen-lowering drugs for 3 or 4 months before surgery, we can monitor treatment response and then specifically tailor surgical and postsurgical treatment based on this response.”