In the context of hormonal therapy, what effect does oral tamoxifen have?

Oral tamoxifen primarily functions as a selective estrogen receptor modulator (SERM) and is widely used in the treatment of hormone-receptor-positive breast cancer. One notable effect of tamoxifen is its impact on the levels of cortisol binding globulin (CBG).

CBG is a protein produced by the liver that binds to cortisol, thereby regulating its availability in circulation. When tamoxifen is administered, it has been observed to increase CBG levels. This increase subsequently leads to enhanced binding of cortisol in the bloodstream, effectively altering the amount of free or active cortisol available for physiological functions. The interaction occurs as a result of tamoxifen's modulation of various hormonal pathways, which can influence liver function and plasma protein synthesis.

This understanding is critical in the context of treating patients, particularly postmenopausal women, who may be on tamoxifen therapy, as their cortisol metabolism and the resultant physiological effects can differ from those in the general population. Understanding how tamoxifen affects CBG is important for anticipating any potential side effects or therapeutic implications related to cortisol availability and action.