An increase in breast cancer incidence has been linked to the use of both estrogen and progestin as a therapy.
The study also found that prognosis is similar for combined hormone therapy's users and nonusers, suggesting that death from breast cancer may be higher for hormone therapy users as well.
In the Women's Health Initiative (WHI) randomized trial, estrogen plus progestin was associated with an increase in both breast cancer incidence and mortality.
They found that breast cancer incidence was higher in estrogen plus progestin users than incidence in nonusers.
Women who started hormone therapy closer to menopause had a higher breast cancer risk with a weakening influence as the time from menopause increased.
The researchers wrote that because survival after breast cancer diagnosis did not differ between estrogen plus progestin users and nonusers, the higher breast cancer incidence of those using estrogen plus progestin may lead to increased breast cancer mortality on a population basis.
The study has been published in the Journal of the National Cancer Institute.