PGR and breast cancer: The risk-reducing effect of breast cancer by tamoxifen was promoted by estrogen-alone HRT,71 which would induce PgR and thus potentiate the anti-breast-cancer effect of tamoxifen via suppression of progesterone signaling.174–176 Thus, higher use of tamoxifen, combined with progestin-limited estrogen HRT, may have also mitigated the risk of breast cancer recurrence in the Stockholm trial.