ESR1 and endometrioid adenocarcinoma: Marked expression of ERα was detectable with IHC in 96.7% of specimens of normal endometrial tissue, 93.3% of endometrial hyperplasia samples, 73.3% of atypical endometrial hyperplasia samples, and 45.5% of endometrioid adenocarcinoma samples (P < 0.001, Table S4, Fig. 1).