Among the 5,787 women, 2,274 did not have oophorectomy, 2,123 had already had the surgery when they began the study, and 1,390 underwent oophorectomy during the study follow-up period. After an average follow-up period of 5.6 years (with some women followed as long as 16 years), 186 women developed either ovarian, fallopian tube, or peritoneal cancer.
Overall, the investigators found that oophorectomy reduced the risk of ovarian cancer by 80 percent. For women who carry a BRCA1 mutation, the authors estimate that delaying the surgery until age 40 raised the risk of ovarian cancer to 4 percent; ovarian cancer risk increased to 14.2 percent if a woman waited until age 50 to have the surgery. In contrast, only one case of ovarian cancer was diagnosed before age 50 among BRCA2 mutation carriers in this study. By comparison, the lifetime risk of ovarian cancer in all women (including those without BRCA mutations) is only 1.4 percent.
Of the 511 women who died during this study, 333 died of breast cancer, 68 from ovarian, fallopian tube, or peritoneal cancers, and the remainder from other causes. Prophylactic oophorectomy reduced the risk of death by any cause by 77 percent (largely by lowering the risks of ovarian, fallopian tube, peritoneal, and breast cancers). Dr. Narod noted that the 77-percent risk decrease is even greater than the benefit of chemotherapy, and was equally strong for both BRCA1 and BRCA2 mutation carriers.
In a prior study by this group, oophorectomy was also sho
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American Society of Clinical Oncology