Abstract

HERE IS CONSIDERABLE EVIdence from observational studies, 1 and now from a randomized controlled trial, the Women's Health Initiative (WHI), 2 that use of combined estrogen and progestin hormone replacement therapy (CHRT) is associated with an increased risk of breast cancer.Specifically, a pooled analysis of 51 observational studies found that current users of CHRT or progestin alone for 5 years or longer had a 53% increase in risk of breast cancer, 1 and after 5.2 years of follow-up the WHI reported that CHRT was associated with a statistically nonsignificant 26% increase in breast cancer risk. 2 However, few studies have evaluated the effects of very long durations (Ն15 years) of CHRT use on breast cancer risk.Two studies found that use of CHRT for 5 years or longer was associated with an increased risk of breast cancer (although use for 10 years or longer did not further increase the magnitude of these risks), 3,4 but another reported that only use of CHRT for 10 years or longer was associated with an increase in risk. 5Also, the WHI evaluated use of the progestin component of CHRT in a continuous (daily) manner, and thus its results may not pertain to other patterns of CHRT use.