ERBB2 and cancer: Although breast tumours are classified in six subtypes (Luminal A, Luminal B, ERBB2/HER2+, Basal-like, Claudin-low and Normal breast-like), only three different subtypes of cancer cell lines are identified based on gene expression; Luminal, Basal A and Basal B. Even though a significant discrepancy of subtypes between primary tumours and cell lines exist, comparison have shown that cell lines mirror both the genomic heterogeneity and the recurrent genome copy number abnormalities found in primary tumours.