ERBB2 and breast cancer: The luminal A subtype includes ER-positive and/or PR-positive, HER2-negative breast cancers; luminal B subtype includes ER-positive and/or PR-positive, HER2-positive breast cancers; basal subtype includes ER-negative, PR-negative, HER2-negative breast cancers which may also be positive for EGFR, and HER2-enriched subtype includes ER-negative, PR-negative, and HER2-overexpressing breast cancers.