<prompt> Answer this question truthfullyWhat is the definition of a selective estrogen receptor modulator SERM in terms of its effect on estrogen receptors in the breast and uterus, and what is an example of a SERM?  <response>: <reason> A selective estrogen receptor modulator SERM is a medication that has estrogen antagonist activity on the breast and uterus. An example of a SERM is raloxifene. 