In addition to HER2 overexpression or amplification, the most reported predictive biomarkers for patients with HER2-positive cancer include the HER2-enriched subtype and the presence of phosphatase phosphoinositol-3 (PI3) kinase (PIK3CA) mutations, tumor-infiltrating lymphocytes (TILs), hormone receptors (HRs), and Ki-67. The gene discussed is ERBB2; the disease is cancer.