By David Liu, PHD

Sunday Oct 7, 2012 (foodconsumer.org) -- If you have ever paid attention to the cancer-causing effects of hormones, you might have gotten an impression from studies or news reports that estrogen plus progestin is safer than estrogen alone as a hormone therapy when it comes to their effect on the risk of breast cancer.

Hormone replacement therapy is used to help relieve menopause symptoms like night sweats and hot flashes in postmenopausal women.   This therapy has been associated with increased risk of breast cancer and heart disease.  But some studies suggest that estrogen plus pregstin does not increase the risk.

A new study in The New England Journal of Medicine has now found evidence to suggest that adding progestins does not lower the risk of breast cancer induced by estrogen in postmenopausal women.

The study led by Graham A. Colditz, M.B., B.S. and colleagues was intended to establish an association between use of hormones and the risk of breast cancer in postmenopausal women.  The study was based on data from participants in the Nurses' Health Study during an extended follow-up until 1992.

During the follow-up, postmenopausal women were asked to complete questionnaires every two years to update their status of their menopause, use of estrogen and progestin hormones, and any diagnosis of breast cancer. And during the follow-up, 1935 cases of breast cancer were identified.

Menopausal women who were currently using estrogen alone or estrogen plus progestin were found at a 32 or 41 percent increased risk of breast cancer, respectively, compared with those who never use any hormone therapy.

Current hormone users who had been using the hormone therapies for 5 to 9 years faced an increase in the risk of breast cancer as were those current users who had been using hormones for greater than 10 years.  The risk in breast cancer was increased in both groups by 46 percent.

Among older postmenopausal women, those who had been using postmenopausal hormone therapy for five or more years were 71 percent more likely to develop breast cancer, compared with those who did not use hormones.  

Those who had been taking estrogen for five or more years were at 45 percent increased risk of dying from breast cancer.

The researchers concluded "The addition of progestins to estrogen therapy does not reduce the risk of breast cancer among postmenopausal women. The substantial increase in the risk of breast cancer among older women who take hormones suggests that the trade-offs between risks and benefits should be carefully assessed."

According to an authoritative organization, two major risk factors for breast cancer are hormone replacement therapy and medical radiation.

Breast cancer is in many cases preventable and the disease is expected to hit more than 230,000 women in the United States in 2012 and kills 37,000 women each year in the U.S.