ESR1 and breast cancer: A total of 61.4% of the patient collective had histological invasive carcinoma of no special type (NST); 81.7% of BC patients were ER-positive, whereas 62.6% of patients were PR-positive; 52.2% of patients had a low-grade carcinoma (G1–G2 = 52.2%, G3 = 47.7%) and 64.3% were staged with a tumor size smaller than 2 cm (pT1: 64.3%, pT2–pT4: 35.6).