ESR1 and endometrial cancer: Tamoxifen, a selective estrogen receptor modulator (SERM), may be an option for these very young women, but it is associated with significant side effects (e.g., hot flashes, endometrial cancer, venous thromboembolic disease, depression, diminished sexual functioning, etc.), and there are no trial data on its efficacy in women under the age of 35 [32,118].