Influence of tamoxifen on the tumor content of steroid hormone receptors (ER, PgR and AR) in patients with primary breast cancer.

A possible influence of tamoxifen (TAM) treatment on the measurable content of some steroid hormone receptors (i.e. ER, PgR, AR) from primary breast cancers has been evaluated. In eleven postmenopausal women, two biopsies were taken from the same tumor, the first biopsy before starting endocrine treatment, and a second biopsy after 8 weeks on tamoxifen treatment. A significant decrease in ER content was found both using a ligand binding (p < 0.005) and an enzyme immunoassay (p < 0.02). As for the PgR and AR content, no significant changes in the mean content were found.