GPER1 and endometrial cancer: Interestingly, within our endometrial cancer repository, we identified six patients who received tamoxifen-based therapy for recurrent endometrial cancer, and of these only one patient (case 1, above, with low GPER expression) experienced a complete response; in contrast, all nonresponders displayed increased GPER expression (defined as expression above the mean [37]) by immunohistochemistry of paraffin-embedded tumor samples (Fisher's P = 0.03), suggesting that a lack of or low GPER expression may be a predictor of tamoxifen responsiveness in endometrial cancer.