Letrozole

Letrozole is an aromatase inhibitor used mainly in postmenopausal women with hormone-receptor-positive breast cancer. It works by blocking the enzyme that converts other hormones into estrogen, dropping estrogen levels in the body to very low levels. This helps starve estrogen-sensitive cancer cells, but estrogen also protects bone, so cutting it off this sharply affects bone remodeling too.

Because estrogen normally slows down bone breakdown, letrozole's effect on estrogen means bone loss can speed up while someone is taking it, more than with some other breast cancer therapies like tamoxifen, which has some estrogen-like activity that is gentler on bone. This is why doctors typically order a baseline DEXA scan before or early in treatment and repeat it periodically to track bone mineral density changes over time.

If bone loss is significant or fracture risk is high, a prescriber may add calcium and vitamin D support or consider a bone-protective medication such as a bisphosphonate or denosumab alongside letrozole. Any decisions about starting, stopping, or adjusting letrozole or adding bone medications belong to your oncologist or prescribing doctor, since they balance cancer treatment goals against bone health.