Pre-emptive removal of breasts or ovaries in women with two common breast cancer genes can sharply reduce the risk of contracting cancer and dying, even if a woman has already been diagnosed with breast cancer, a new study confirms.

Researchers were already confident that such prophylactic surgeries reduce the risk of cancer, but the new study, reported yesterday in the Journal of the American Medical Association, is the largest such investigation to date and the first to differentiate the benefits based on which gene a woman has and whether or not she has already had cancer. It is also the first to show a survival benefit.

Removal of the ovaries and ovarian tubes in women with either the BRCA1 or BRCA2 genes can almost completely eliminate the risk of ovarian cancer and reduce the risk of breast cancer by about two-thirds, the study found.

Removal of breasts can reduce the risk of breast cancer by as much as 85 percent. Either procedure reduces the risk of dying by at least two-thirds.

"We already knew intuitively that removing breasts reduces the risk of breast cancer, but this is the first paper that actually shows it contributes to a survival benefit," said Dr. Jane Kakkis, surgical director at MemorialCare Breast Center at Orange Coast Memorial Medical Center in Fountain Valley, Calif., who was not involved in the study. "That's a big difference in terms of helping patients make a difficult decision."

"This paper reminds us that genetic testing can save lives," added Dr. Kenneth Offit, chief of the clinical genetics service at Memorial Sloan-Kettering Cancer Center in New York, who also was not involved in the study. "If a woman or a man has a family history of breast, ovarian or prostate cancer, it is wise to speak to a physician about genetic testing, (which can) lead to surgical options that will decrease the risk of subsequent cancer."

Women who have either of the two BRCA genes have a lifetime risk of 56 percent to 84 percent of developing breast cancer. Women with the BRCA1 gene have a 36 percent to 63 percent risk of ovarian cancer, while those with BRCA2 have a 10 percent to 27 percent risk.

Prophylactic mastectomies sharply reduce the risk of breast cancer by surgically removing the bulk of tissue in which such tumors arise.

Prophylactic removal of the ovaries and tubes, a procedure called salpingo-oophorectomy, not only nearly eliminates the risk of ovarian cancer by removing virtually all of the tissue in which it can arise, but also reduces the risk of breast cancer by sharply reducing production of estrogen, which fuels the growth of breast tumors.

In the study, a team headed by Dr. Timothy R. Rebbeck and Dr. Susan M. Domchek of the University of Pennsylvania School of Medicine studied 2,482 women who had been diagnosed as BRCA carriers between 1974 and 2008.