Hormone therapy and breast cancer regression

As soon as women quit hormone therapy, their rates of new breast cancer decline, supporting the hypothesis that stopping hormones can lead to tumor regression, according to Cancer Epidemiology, Biomarkers, & Prevention. As part of the national Breast Cancer Surveillance Consortium, researchers studied 741,681 woman-years of data on 163,490 women aged 50-79 who had no prior history of breast cancer.

This is the first study to look over time at screening mammography use among individual women by their hormone therapy status linked with their breast cancer diagnoses. Previous research has shown a rapid decline in new breast cancers -- and also in use of hormone therapy and of screening mammography -- since 2002, when the Women's Health Initiative published that breast cancer rates were higher in women taking estrogen and progestin than in those taking either a placebo or only estrogen. Some have suggested that the decline in use of hormone therapy may have caused the fall in the breast cancer rate, perhaps by making tumors regress,

Others have countered that the explanation for the declines in both breast cancer and hormone use might instead be that because former hormone users are less concerned about breast cancer or see their doctors less often, they may get less screening mammography than do women who have never taken hormones. These results refute that hypothesis. Differences in rates of screening mammography don't explain the declines in rates of the incidence of invasive breast cancer among women who've stopped using hormone therapy.