Pathologists determine this score by examining immunohistochemically stained tumor tissue sections and applying the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines, which assign each tumor cell to one of four HER2 categories (0, 1+, 2+, or 3+) based on membrane staining patterns.5 The gene discussed is ERBB2; the disease is neoplasm.