ESR1 and breast cancer: We recently published a study showing the strong interaction between the breast cancer molecular subtypes classification as determined by estrogen receptor (ER) and HER2 immuno-staining (ER positive HER2 negative | ER negative HER2 negative | ER negative HER2 positive | ER positive HER2 positive) and the risk of metastatic axillary sentinel lymph node [16].