Use of hormone replacement therapy and risk of breast cancer

U.K. researchers explored the risk of breast cancer in women exposed to different hormone replacement therapies (HRTs) for different durations of use. The study included 98,611 women aged 50–79 years who were diagnosed with breast cancer between 1998 and 2018 and 457,498 matched controls. Approximately one-third of women in each cohort had used HRT prior to 1 year before the index date. The risk of a breast cancer diagnosis was generally greater, however, in cases where HRT involved combination treatments and where it was used for extended periods of time. Exposure to estrogen-only or estrogen-progestogen therapy for 5 years or more, for example, both correlated to elevated risk of breast cancer when compared with zero past use of HRTs. On the other hand, previous long-term use of estrogen-only HRT or past short-term use of estrogen-progestogen were not associated with higher risk.