Hormone Therapy Linked to Breast Cancer
Considerable evidence links hormone replacement therapy to the development of breast cancer, although few studies have examined the consequences of long-term hormone use on breast cancer risk.
Also, most previous research failed to evaluate the potential association between patterns of use and risk.
To evaluate relationships between durations and patterns of combined (estrogen and progestin) hormone replacement therapy (CHRT) use and risk of breast cancer, researchers studied 975 women (65-79 years of age) diagnosed with invasive breast cancer, and 1,007 controls recruited from the general population. Each patient was interviewed by a trained interviewer and completed a standardized questionnaire. Detailed histories of all episodes of HRT use; total duration; brand; dosage; and pattern of use (i.e., days per month) were obtained, as were data on reproductive history, body size, medical history and family history of cancer. A life-events calendar and a photo book of HRT medications used in the U.S. were provided to each participant to enhance recall.
Users of combined hormone replacement therapy had nearly twice the risk of developing breast cancer as nonusers, with the greatest risk observed in women using CHRT for five years or longer. Women using CHRT for five to 14.9 years had the highest risk for carcinoma, including a 1.5-fold risk for invasive ductal carcinoma and a 3.7-fold risk for lobal carcinoma. Similar associations were
noted in users of both sequential and continuous CHRT. By comparison, women who used exclusive estrogen replacement therapy had no appreciable increase in breast cancer risk compared with nonusers, regardless of when they had last used HRT or their overall duration of use.
The authors note that their findings add to mounting evidence linking the use of combination hormone replacement therapy to increased risk of breast cancer, adding that this increased risk appears to manifest within several years of initiating CHRT use and exists whether women choose continuous or sequential therapy.
Li CI, Malone KE, Porter PL, et al. Relationship between long durations and different regimens of hormone therapy and risk of breast cancer. Journal of the American Medical Association
, June 25, 2003:289(24), pp3254-63.