Breast case scenario.

Top Line: The use of menopausal hormone replacement therapy (MHT) skyrocketed in the late 90’s, advertised as a way of preventing heart disease and bone loss in women.
The Study: That all came crashing down when the Women’s Health Initiative trials demonstrated excess heart disease, stroke, blood clots, and breast cancer with combined MHT. Yikes. While long-term preventive MHT is no longer recommended, that doesn’t mean short-term MHT can’t help transition younger women through the beginnings of menopausal symptoms. The problem is that data is limited on the effect of both timing and duration of different MHT formulations. This collaborative group study takes an in-depth look at how breast cancer risk is impacted by patient age as well as duration and cessation times of MHT. First, they found that any type of MHT (except vaginal estrogen) was associated with an increase in the risk of breast cancer. That risk increased with, and persisted in proportion to, duration for as long as 10 years after stopping MHT. For example, combination MHT x 5 years in an average weight woman resulted in a 2% absolute increase in breast cancer at 20 years. Estrogen-alone MHT x 5 years resulted in a 0.5% absolute increase in breast cancer at 20 years. These rates roughly double for double the duration. Interestingly, the excess risk from MHT was attenuated by weight—but not how you might think. While lean women saw increases in breast cancer risk with MHT, MHT (particularly estrogen alone) didn’t really seem to increase the already-elevated baseline risk among obese women.
TBL: Systemic (read: not topical) hormone replacement in post-menopausal women increases the risk of breast cancer in proportion to duration and inverse proportion to BMI. | Collaborative Group on Hormonal Factors in Breast Cancer, Lancet 2019


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