What is the primary function of tamoxifen?

Tamoxifen primarily functions as an estrogen antagonist in breast tissue. It is a selective estrogen receptor modulator (SERM) that binds to estrogen receptors and competes with estrogen for these sites in breast cells. By blocking estrogen's action in breast tissue, tamoxifen helps to inhibit the growth of estrogen-dependent tumors, making it a critical component in the treatment of hormone receptor-positive breast cancer.

In addition to its antagonistic effects in breast tissue, tamoxifen has agonistic properties in other tissues, such as the uterus and bone, where it can promote estrogen-like effects. This selective action illustrates its role as a therapeutic agent, particularly in patients with estrogen receptor-positive breast cancer.

The other options refer to completely distinct mechanisms: inhibiting xanthine oxidase is relevant in treating gout, 5α reductase inhibitors are used primarily for conditions like benign prostatic hyperplasia and male pattern baldness, and carbonic anhydrase inhibitors are utilized for conditions such as glaucoma and altitude sickness. These further emphasize the unique role of tamoxifen in the context of breast cancer treatment.