Risk of Breast Cancer Decreases After Stopping Hormone Treatment

The Women's Health Initiative (WHI) studied the use of the hormones, estrogen and progestin.  In 2002 a report of that study was released.  In that trial one group received 0.625 mg of estrogen plus 2.5 mg of progestin daily.  A second group received placebo.  There were fewer breast cancer diagnoses in the group receiving estrogen plus progestin than in the placebo group in the initial 2 years of the study, but the number of diagnoses increased over the course of the 5.6-year intervention period. The elevated risk decreased rapidly after both groups stopped taking the study pills. In the observational study, the incidence of breast cancer was initially about two times as high in the group receiving menopausal hormones as in the placebo group, but this difference in incidence decreased rapidly in about 2 years, coinciding with year-to-year reductions in combined hormone use.

The conclusion is that the increased risk of breast cancer associated with the use of estrogen plus progestin declined markedly soon after discontinuation of the hormone therapy.