Is “Basal-like” Carcinoma of the Breast a Distinct Clinicopathologic Entity? A Critical Review with Cautionary Notes

This review deals with studies that have used cDNA microarrays and immunohistochemistry to identify a subtype of breast carcinoma recently known as “basal-like” carcinoma. The key breast carcinoma studies are critically discussed to highlight methodological problems in cohort selection, definitions, interpretation of results, and statistical analysis. It concludes that “basal-like” carcinomas do not reflect a single, biologically uniform group of breast cancers and show significant variations in their phenotypes, grades, immunoprofiles, and clinical behavior, just as a wide range of subtypes and behaviors is observed among epithelial/luminal-derived breast carcinomas. Welldesigned studies with comparison of low grade non-basal versus low grade basal and high grade non-basal versus high grade basal carcinomas are necessary before one can be convinced that this subtype represents a distinct clinicopathologic entity.