title: Effect of tamoxifen treatment on estrogen metabolism in postmenopausal women with advanced breast cancer.
abstract: The effect of tamoxifen therapy on plasma estrone and estradiol concentration, urinary excretion of estrone, estradiol, and estriol glucuronides, and metabolism of a tracer of 3H-estradiol was studied in 12 postmenopausal women with metastatic breast cancer. The most striking change observed was consistent increase in the 72-hour urinary recovery of total radioactivity after the tracer, from a mean of 47% to a mean of 61% of the dose. This increase was accounted for by a corresponding increase in the recovery of total glucuronide radioactivity, from a mean of 32% to a mean of 44% of the dose; there was no change in the proportions of estrone, estradiol, estriol, or 2-hydroxyestrone in the glucuronide fraction. The most likely explanation for this finding is that the estrogen-receptor-blocking effect of tamoxifen decreases estrogen uptake by various tissues and permits the estrogen to be excreted in the urine instead. There was also a small but consistent and significant decrease in plasma estrone (from 47 to 36 pg/ml) and estradiol (from 15 to 13 pg/ml), with no change in urinary excretion of estrogen glucuronides. The drop in plasma estrogen levels without a decrease in estrogen production suggests that tamoxifen may increase the metabolic and/or renal clearance of estrogen metabolites. There was no correlation between the observed effects of tamoxifen and the pretreatment estrogen-receptor status of the patient or her response to tamoxifen therapy.
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004958:Estradiol / Q000097:blood; D004964:Estriol / Q000031:analogs & derivatives / Q000652:urine; D004967:Estrogens / Q000378:metabolism*; D004970:Estrone / Q000097:blood / Q000652:urine; D005260:Female; D006801:Humans; D008593:Menopause; D008875:Middle Aged; D013629:Tamoxifen / Q000494:pharmacology*
chemical_list: D004967:Estrogens; D013629:Tamoxifen; C032095:estriol glucuronide; D004970:Estrone; D004958:Estradiol; D004964:Estriol