Contemporary classification of breast cancer

Abstract

Studies of breast cancers using gene expression profiling have identified several major subtypes. The best characterised are luminal A, luminal B, HER2-enriched and basal-like, which differ in their gene expression patterns, clinical features, response to treatment and outcome. One of the most novel findings has been the characterisation of basal-like breast cancers, which are often high-grade invasive ductal carcinomas with solid architecture, high mitotic rate, stromal lymphocytic infiltrate, pushing border, geographic necrosis and/or a central fibrotic focus. They are typically ER-, PR-, and HER2-negative and have a poor prognosis. Interestingly, some tumours with a favourable prognosis also cluster in the basal-like group (adenoid cystic and secretory carcinomas). Approximately 70–80% of basal-like tumours are clinically triple negative and vice versa.