ERBB2 and carcinoma: The new therapeutic options have led to an increased proportion of patients with metastatic breast cancer who may benefit from anti-HER2 therapy: in addition to patients with classically strongly HER2-positive carcinomas (approximately 15%) [15], a large group of patients with HER2-low-expression tumors (approximately 50%, depending on the study cohort) might also benefit from anti-HER2 therapy [29].