Possible Interaction: Progestins and Tamoxifen

“Our results indicate that addition of the progestogen significantly alters the metabolism of tamoxifen over a six-month period.”

“The hypothesis that 17 beta-estradiol or tamoxifen (TAM) can potentiate clinical response of endometrial cancer treated with progestin was tested in an ovariectomized nude mouse system, using a sex steroid receptor-positive and a receptor-negative human endometrial carcinoma.”

“Based on the finding that TAM induces functional PR, we predict that steroid receptor-positive endometrial carcinoma may show a greater response rate to combined, long-term treatment with TAM and progestin.”

“A higher risk in women receiving estrogen replacement therapy (ERT) or tamoxifen has been suspected, and remissions following treatment with progestins have been reported in case studies.”

“This relatively very low ER and PR content may be attributed to the antagonistic effect of progestogens on the "priming" estrogen-like effect of tamoxifen on the endometrium.”

“These data show that postmenopausal breast cancer patients who received progestogens for < or = 3 months, and who concomitantly took tamoxifen , had a uniform decidual reaction in all uteri.”

“Adapted cells were growth inhibited by oestradiol, 4-hydroxy tamoxifen and medroxyprogesterone acetate, but despite elevated progesterone receptor expression the progestin was only marginally more inhibitory than in the parent line.”

“Current studies aim to relate RP levels to objective remissions of metastases after progestin therapy, and attempts are being made to increase RP with tamoxifen before treatment with progestins or assaying for RP.”

“Combined treatment with tamoxifen and progestin effectively controlled human endometrial tumor growth in the nude mouse model.”

“On the other hand, the addition of HRT containing progestins could also minimize the risk of endometrial cancer associated with tamoxifen.”