Long-Term Use of Estrogen Hormone Therapy Linked to Higher Risk for Breast Cancer

In a landmark study, researchers have linked the long-term use of estrogen plus progesterone and estrogen-only hormone therapy with a higher risk for developing breast cancer.

“It’s already been confirmed that patients shouldn’t be undergoing estrogen plus progesterone hormone therapy (HT) for the long term,” said Wendy Y. Chen, M.D., M.P.H., associate physician at Brigham and Women’s Hospital and assistant professor in medicine at the Breast Cancer Oncology Center at the Dana-Farber Cancer Institute in Boston, Mass. “What we found is that people should also be careful about longer-term use of estrogen-alone HT.”

In previous studies, she said, researchers only evaluated risks associated with less than 10 years of HT use. Chen presented the findings at the AACR Annual Meeting 2012, held here March 31 - April 4.

Using data from the Nurses’ Health Study, the researchers evaluated follow-up data collected during 1980 through 2008 from postmenopausal female registered nurses who were aged 30 to 55 years old in 1976.

Chen and colleagues found that the risk for breast cancer, when compared with women who did not use HT, was 88 percent higher in women who had taken estrogen plus progesterone for 10 to 14.9 years; the risk increased more than twofold for women who used estrogen plus progesterone therapy for 15 to 19.9 years. For women who used estrogen-only HT, researchers found a 22 percent increased risk for breast cancer if used for 10 to 14.9 years and a 43 percent greater risk associated with 15 to 19.9 years of use.

Researchers also found that the risk did not plateau for either kind of HT. “There’s a continued effect over time. The longer you use it, the higher the risk,” said Chen.

Breast cancer Risk factors A risk factor is anything that makes it more likely you'll get a particular disease. But having one or even several risk factors doesn't necessarily mean you'll develop cancer — many women who develop breast cancer have no known risk factors other than simply being women.

Factors that are associated with an increased risk of breast cancer include:

• Being female. Women are much more likely than men are to develop breast cancer.
• Increasing age. Your risk of breast cancer increases as you age. Women older than 55 have a greater risk than do younger women.
• A personal history of breast cancer. If you've had breast cancer in one breast, you have an increased risk of developing cancer in the other breast.
• A family history of breast cancer. If you have a mother, sister or daughter with breast cancer, you have a greater chance of being diagnosed with breast cancer. Still, the majority of people diagnosed with breast cancer have no family history of the disease.