SAN ANTONIO — Prophylactic mastectomy results in an adjusted 90% reduction in the risk of breast cancer, according to new results from the world's largest prospective study of the procedure.
During a median follow-up of 4.1 years in the Rotterdam Prophylactic Mastectomy Study, there has been just one case of breast cancer detected among 124 high-risk BRCA1 or BRCA2 mutation carriers who underwent the surgery, reported Jan G.M. Klijn, M.D., during a breast cancer symposium that was sponsored by the Cancer Therapy and Research Center.
In contrast, 23 of 202 similarly high-risk women who had opted for aggressive surveillance in lieu of prophylactic mastectomy have developed the malignancy during a median 3.6 years' follow-up.
Two of the women died of breast cancer before age 30, according to Dr. Klijn of Erasmus University, Rotterdam, the Netherlands.
Eighty percent of the participants in the study carried a BRCA1 mutation. The rest of the participants were found to be BRCA2 positive, the researchers said.
Results of the Dutch study are consistent with those of a retrospective Mayo Clinic study and a smaller prospective study.
Collectively, there have been three reported cases of breast cancer following prophylactic mastectomy in 255 BRCA1 or BRCA2 mutation carriers in the studies. Two of the three cases involved metastatic breast cancer. The capacity to matastasize is a characteristic of all malignant tumors.
In each of the three studies, prophylactic mestectomy reduced the risk of breast cancer by at least 90%. Those results make prophylactic mastectomy the most effective available preventive measure.
In comparison, chemopreventive tamoxifen therapy was reported to yield an approximate 40% reduction in breast cancer risk. Patients who have prophylactic oophorectomy are said to achieve a 50% reduction in the risk of breast cancer, Dr. Klijn said.