ESR1 and breast cancer: Almost all patients included in the study group had an estrogen receptor (ER) positive/HER2 negative breast cancer (67.8%), 27 (9.7%) patients had a ER positive/ HER2 positive breast cancer, 14 (5%) had an HER2 positive/ER and PgR negative and 26 (8.2%) had a triple negative breast cancer.