ERBB2 and breast cancer: Breast cancer can be further classified through gene expression profiling into PAM50 (Prosigna, distinct subtypes (luminal A, luminal B, HER2-enriched, basal-like, and normal-like2), with significant differences in prognosis and response to treatment.3 Oncotype DX4 (Genomic Health, Redwood City, CA) and MammaPrint5 (Agendia, Irving, CA) are commercially available gene expression assays that determine a risk score that can be used to tailor treatment.