Triple negative and basal-like breast cancer: one or many diseases? Implications for surgical pathologists

Take home messages The majority of basal-like breast cancers have a triple negative phenotype and the vast majority of triple negative cancers display a basal-like transcriptome, however the two are not synonymous. Basal-like and triple negative breast cancers comprise a heterogeneous group of diseases, which are characterised by a constellation of morphological features. Not all basal-like and triple negative breast cancers have a poor outcome. The precursors of invasive breast carcinomas of basal-like and triple negative phenotype include ductal carcinoma in situ harbouring a similar phenotype and, possibly, a subgroup of microglandular adenosis. A subgroup of basal-like and triple negative breast cancers displays an exquisite sensitivity to anthracycline-based neoadjuvant chemotherapy. Defects in the p53, pRB and p16 pathways are found in a significant proportion of basal-like and triple negative cancers. BRCA1 pathway dysfunction is found in a substantial proportion of basal-like and triple negative breast cancers and can be exploited therapeutically (e.g. inhibitors of the PARP enzyme and cross-linking agents)