ESR1 and breast carcinoma: Accordingly, oncology studies demonstrated that patients with a HER2-negative hormone receptor-positive (ER+ or PR+) status are more prone to bone metastases45 Here, we provided new features of the MRMT-1 tumor cells used to model metastatic bone pain, reporting that MRMT-1 rat breast carcinoma cells are ER-positive and HER2-negative with a high Ki-67 expression and a tamoxifen sensitive profile.