In the overall cohort (N = 547), the proportion of HER2-low cases was 34.2% (n = 187) of primary breast cancer samples and 37.3% (n = 204) of recurrent/stage IV samples, accounting for the 45.0% and the 48.9% of the entire HER2-negative primary breast cancer and recurrent cohorts, respectively. The gene discussed is ERBB2; the disease is breast cancer.