Influence of droloxifene (3-hydroxytamoxifen), 40 mg daily, on plasma gonadotrophins, sex hormone binding globulin and estrogen levels in postmenopausal breast cancer patients.

Droloxifene (3-hydroxytamoxifen) is a novel antiestrogen currently undergoing clinical investigations for treatment of breast cancer patients. We measured plasma levels of sex hormone binding globulin (SHBG) and the gonadotrophins (LH and FSH) at baseline and after 3 months on treatment in a group of fourteen postmenopausal women treated with droloxifene 40 mg daily. Plasma levels of estrone (E1), estradiol (E2) and estrone sulphate (E1S) were measured in a subgroup of eight patients. Plasma SHBG increased during treatment with droloxifene by a mean value of 16.6% (P < 0.05), while plasma levels of LH and FSH decreased by a mean value of 15.7% (n.s.) and 18.1% (P < 0.05), respectively. Plasma levels of E2 and E1 fell slightly (mean decrease 19.4 and 16.7% respectively, n.s.). On the contrary, plasma levels of E1S increased by a mean value of 23.5% (P = 0.068). The ratio of E1S to E1 and E1S to E2 increased by a mean value of 48.3% (P < 0.025) and 53.2% (P < 0.025), respectively. The effect of droloxifene 40 mg daily on plasma levels of SHBG resembles what is seen during treatment with tamoxifen but occurs to a smaller extent. Contrary to tamoxifen, droloxifene caused a minor suppression of plasma LH levels, suggesting droloxifene to have less estrogen agonistic effects on the pituitary.