According to the results of a study conducted in Italy and published in the Annals of Oncology, risk of breast cancer increases as duration of postmenopausal hormone use increases, and risk of colorectal cancer decreases.
Postmenopausal hormone therapy with either estrogen alone or estrogen plus progestin effectively manages several common menopausal symptoms. However, large clinical trials conducted as part of the Women's Health Initiative (WHI) raised concerns about the health risks of these therapies. In 2002, for example, it was reported that combined estrogen plus progestin increases the risk of breast cancer, heart disease, stroke, and blood clots. Women taking estrogen plus progestin had fewer fractures and were less likely to develop colorectal cancer, but these benefits were thought to be outweighed by the risks for most women.
To explore the relationship between duration of postmenopausal hormone use and risk of cancer, researchers conducted a study among more than 73,000 Italian women between the ages of 45 and 75 years.
The study was restricted to women who had filled at least one prescription for postmenopausal hormones. The study included oral medications as well as transdermal medications such as gels, creams, and patches. The researchers were not able to distinguish between women taking estrogen alone and women taking estrogen plus progestin. Because relatively few women in Italy have had a hysterectomy, however, the researchers state that their results mainly reflect the effect of combined estrogen plus progestin therapy.
- Compared to women who used postmenopausal hormones for less than six months, women who used them for more than two years were 34% more likely to develop breast cancer and 22% less likely to develop colorectal cancer.
- Use of oral hormones appeared to be more strongly linked with breast cancer risk than use of transdermal hormones; both formulations, however, increased risk.
These results are generally consistent with previous studies, and provide additional evidence that use of combined postmenopausal hormones increases the risk of breast cancer and decreases the risk of colorectal cancer.
 Rossouw JE, Anderson GL, Prentice RL et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA. 2002; 288:321-33
 Corrao G, Zambon A, Conti V et al. Menopausal hormone replacement therapy and cancer risk: an Italian record linkage investigation. Annals of Oncology. 2008;19:150-156.