When I am seeing someone who has menopausal symptoms, bad enough to seek relief, I am asked almost 100% of the time if the bio-identicals I am suggesting will increase the risk of cancer. I explain the differences between progestin, a synthetic chemical implicated in cancer, and progesterone, a naturally occurring hormone. I explain why estrogen supplementation, in addition to progesterone, is so useful, and as far as I can see from the literature, not implicated in increased breast cancer risks,except for a subset of cancer patients who had estrogen dependent tumors. There aren’t random controlled studies of any importance yet,though, so a woman should be collaborating with her provider to be involved in her own care decisions.
This article by Jeffrey Dach gives a good overview, with cited references.
Bioidentical Hormones for Breast Cancer Survivors by Jeffrey Dach MD