(Ivanhoe Newswire) -- Taking estrogen plus testosterone therapy to treat menopause symptoms may increase a woman's risk of breast cancer.

Researchers from Brigham and Women's Hospital and Harvard Medical School in Boston looked at the long-term effects of the combination treatment in 121,700 women in the Nurses' Health Study. During 24 years of follow-up -- from 1978 to 2002 -- there were 4,610 cases of breast cancer among postmenopausal women.

Researchers found among women who went through menopause naturally, the risk of breast cancer was nearly 2.5-times greater among those who took estrogen plus testosterone than in women who had never had any hormone therapy. Results also reveal participants who took the combination therapy had a 77-percent higher risk of developing breast cancer than women who had never used hormones -- higher than the increased risk in women who took estrogen (15 percent) or in those who took estrogen plus progestin (58 percent).

Researchers say enzymes in the breast tissue may convert testosterone to estradiol -- an estrogen-like hormone that may contribute to the development of breast cancer.

The authors are concerned because the number of women who used the combined estrogen and testosterone therapy increased dramatically -- from 33 in 1988 to 550 in 1998.

They write, "Given the substantial evidence implicating combined estrogen plus progestin therapy in breast cancer and the results of the present study regarding estrogen plus testosterone therapy, women and their physicians should reconsider use and, more specifically, long-term use of these therapies. Although postmenopausal therapies may provide improvement with respect to sexual functioning, general well-being and bone health, the increased risk of breast cancer may outweigh the benefits."
 

SOURCE: Archives of Internal Medicine, 2006;166:1483-1489