Breast cancer incidence in postmenopausal women using testosterone in addition to usual hormone therapy

Objective: There is now convincing evidence that usual hormone therapy for ovarian failure increases the risk for breast cancer. We have previously shown that ovarian androgens normally protect mammary epithelial cells from excessive estrogenic stimulation, and therefore we hypothesized that the addition of testosterone to usual hormone therapy might protect women from breast cancer.

https://pubmed.ncbi.nlm.nih.gov/15356405/