The median TMB was 3.67 (range 0–32.11) mutations/Mb for HER2-positive, 3.67 (range 0–19.27) mutations/Mb for HER2-low, and 2.75 (range 0–32.11) mutations/Mb for HER2-zero breast tumor. The gene discussed is ERBB2; the disease is breast neoplasm.