Prognosis after breast cancer diagnosis in women exposed to estrogen and estrogen-progestogen replacement therapy.

The association between survival in breast cancer and menopausal hormone treatment prior to diagnosis was analyzed by comparing 261 women who developed the disease in a population-based cohort of estrogen-treated women with 6,617 breast cancer patients without any recorded estrogen treatment drawn from the same population. Complete follow-up was achieved during the 0-9 years of observation. The relative survival rate was significantly higher (p = 0.02), by about 10 percentage points at eight years, in patients who had received estrogen treatment--corresponding to an approximately 40% reduction in excess mortality. The more favorable course could be confirmed only in patients aged 50 years or more at diagnosis (p less than 0.01) and was most pronounced in recent users, that is, in women whose treatment was ongoing (p less than 0.01) or had been discontinued within one year prior to diagnosis. The time from first use to diagnosis and the total duration of estrogen medication were virtually unrelated to survival when the effect of recency was taken into account in multivariate analyses. The authors were unable to examine the effect of stage at diagnosis on the results. Several factors, particularly selection bias and surveillance bias, might have affected the results in favor of the women receiving hormone replacement therapy, but there is a possibility that exogenous female sex hormones affect survival in women with breast cancer.