ESR1 and endometrial endometrioid adenocarcinoma: In 2019, Gaillard et al. reported that ESR1 mutations were detected in 4.4% (24/548) of uterine endometrioid carcinomas vs. 0.2% (1/446) of uterine serous carcinomas and 3.5% (5/144) of ovarian endometrioid carcinomas compared to 0.3% (12/3502) of ovarian serous carcinomas, whereas in an ovarian serous carcinoma both ESR1 Y537S and D538G mutations were detected [39].