Risk Factors

Hormone Replacement Therapy. Several studies have reported a higher risk for breast cancer in postmenopausal women taking hormone replacement therapy (HRT), particularly with prolonged use and with formulations containing both estrogen and progestin. The longer a woman uses HRT, the higher her risk for breast cancer. HRT increases breast cancer density, making mammograms more difficult to read. This can cause cancer to be diagnosed at a later stage.

Progestin has been more strongly associated with risk for breast cancer than estrogen. However, some studies suggest that estrogen-alone HRT can pose a risk for breast cancer when women use it for longer than 10 years. A 2006 study also indicated that combined estrogen and testosterone therapy can double a woman’s risk for breast cancer.

At this time, most experts recommend that women use HRT only for short-term relief of menopausal symptoms. [For more information, see In-Depth Report #40: Menopause]

Breast Abnormalities

Abnormalities or Breast Conditions Suggesting a Higher Risk. Some breast formations or abnormalities should be watched and include the following:

• Dense breast tissue is associated with a higher risk for breast cancer. Studies suggest that in women with highly dense tissue have two to six times the risk of women with the least dense tissue. Genetic factors play a large role in breast density. Hormone replacement therapy also increases breast density.
• Benign proliferative breast disease or atypical cell growth, known as atypical hyperplasia, is a significant risk factor for breast cancer.

Benign Breast Conditions. Benign breast conditions are much more commonly seen on mammograms than cancer. And in the great majority of cases they pose no risk. Some common benign breast abnormalities that pose few or no risks include the following:

• Cysts. These mostly occur in women in their middle to late reproductive years and can be eliminated simply by aspirating fluid from them.

Click the icon to see an image of cysts in the breast.