Which of the following is a selective estrogen receptor modulator (SERM)?

Tamoxifen is identified as a selective estrogen receptor modulator (SERM) due to its unique mechanism of action that allows it to function differently in various tissues. As a SERM, Tamoxifen binds to estrogen receptors, particularly in breast tissue, where it acts as an antagonist, inhibiting the proliferative effects of estrogen on breast cancer cells. However, in other tissues, such as bone or the endometrium, it can act as an estrogen agonist, promoting beneficial effects like maintaining bone density.

Tamoxifen is commonly used in the treatment of hormone receptor-positive breast cancer, especially in premenopausal women. Its selectivity makes it effective for targeting estrogen receptor-positive tumors while providing a favorable profile in other tissues.

In contrast, Fulvestrant is an estrogen receptor downregulator that does not exhibit the same selective agonist/antagonist properties as SERMs. Anastrozole is an aromatase inhibitor that decreases estrogen production, and Goserelin is a GnRH agonist that influences hormone levels through a different mechanism. Each of these alternatives has distinct roles in cancer treatment but does not fit the criteria for a SERM.