ERBB2 and breast cancer: To gain insights into the molecular basis of HER2-low BC, Berrino et al. performed high-throughput molecular analysis on 99 HER2-low BC tissue samples and compared the mutation rates and gene expression profiles of HER2-low BC with those of HER2-negative and HER2-positive BCs in a Memorial Sloan-Kettering Cancer Center BC cohort [24].