Appraisal ofgenomic and biological properties highlight the importance of molecular signallingin tumour biology and in personalising therapeutic decision making,3, , -6 while also providing prognosticinformation on the basis of the molecular phenotype of cancers.7 Such advances have facilitated the clinical substratification of the diseaseinto 4 biologically distinct, clinically relevant, molecular subtypes: Luminal A,Luminal B, Triple Negative, and Human Epidermal Growth Factor Receptor-2 (HER2/neu)overexpressing breast cancers.8 Here, ERBB2 is linked to breast cancer.