This is the first report using RNA-seq data to show that CBX2 is enriched in basal-like and HER2+ tumours and our result is supported by a previous study that also found increased CBX2 expression in basal-like breast tumours in a microarray mRNA breast cancer dataset.22,34CBX2 mRNA expression may therefore serve as a marker of aggressive breast cancer subtypes, such as basal-like carcinomas, which lack a reliable molecular marker. The gene discussed is ERBB2; the disease is breast cancer.