SERM: selective estrogen receptor blocker (modulators)

Tamoxifen is a selective estrogen receptor modulator (SERM). In breast tissue, it antagonizes the estrogen receptor, but in the uterus (endometrium) it acts more like an agonist (i.e., it has estrogen‐like effects) which may stimulate the endometrium and lead to hyperplasia, polyps, and eventually malignant transformation in susceptible cases