Women who take hormone therapy during menopause are more likely to develop breast cancer, and their risk increases the longer they take the drugs, according to a study published Aug. 29 in The Lancet.
Researchers collected data from dozens of studies on the type and timing of menopausal hormone therapy among women from Jan. 1, 1992, to Jan. 1, 2018. The data included over 100,000 women who developed breast cancer after menopause.
They found half of those 100,000 women had taken MHT. Their risk for breast cancer rose the longer they took the drugs, with the risk doubling after five to 14 years. Women who took estrogen-progesterone had a higher risk for breast cancer than those who only took estrogen, and the risk remained even after women stopped taking the drugs.
Women are often prescribed MHT to replace hormones and treat symptoms during menopause, STAT reported. Previous research has suggested a link between MHT and breast cancer, but the new study provides more data on the duration of the risk during and after taking MHT, as well as the risk of taking estrogen as opposed to estrogen-progesterone.
The study does not prove that MHT directly causes breast cancer. Researchers believe the association is due to the drop in hormones that occurs during menopause, which is thought to lower the risk of breast cancer. Using MHT might perpetuate the presence of these hormones in women's bodies and block menopause's protective effects.