Basal cytokeratins and their relationship to the cellular origin and functional classification of breast cancer

Abstract

Recent publications have classified breast cancers on the basis of expression of cytokeratin-5 and -17 at the RNA and protein levels, and demonstrated the importance of these markers in defining sporadic tumours with bad prognosis and an association with BRCA1-related breast cancers. These important observations using different technology platforms produce a new functional classification of breast carcinoma. However, it is important in developing hypotheses about the pathogenesis of this tumour type to review the nomenclature that is being used to emphasize potential confusion between terminology that defines clinical subgroups and markers of cell lineage. This article reviews the lineages in the normal breast in relation to what have become known as the 'basal-like' carcinomas.

Figure 1

Normal breast duct and terminal duct lobular unit (TDLU) stained with antibodies to cytokeratin (CK)5 and CK14. Note the coexpression of these proteins that form a heterodimer. In this example the luminal cells are the dominantly stained population in the TDLU, but in the duct the myoepithelial cells are stained. Great variability can be seen both within the same breast and between specimens.