In a recent study, Denkert and colleagues analyzed tumor biopsies from 3771 breast cancer patients and found that high T cell infiltration predicted a better survival for patients with human epidermal growth factor receptor 2 (HER2)-positive tumors and increased tumor-infiltrating lymphocyte (TIL) concentrations predicted a response to neoadjuvant chemotherapy in all tumors. The gene discussed is ERBB2; the disease is neoplasm.