Table 1.

Intrinsic classification of breast cancer by gene expression profiles and cell surface hormonal expression

ER-positive	ER-low	ER-negative, PR-negative, HER2-negative	Normal breast-like
Luminal A	HER2-enriched	Claudin-low	High stromal content
Luminal B		Basal-like subtype	High lymphocyte infiltration
			True normal epithelial cell contamination

Column headings indicate primary immunohistochemical criteria only (ER-positive and so on; in italics). The subtypes are indicated below each heading. Subtypes in bold exhibit worse prognosis (relapse and mortality). There are four most commonly referred subtypes in the literature: luminal A, luminal B, HER2-enriched and triple-negative basal-like. Additional subtypes that have been proposed are claudin-low in the triple-negative group and normal breast-like, which are subdivided into additional subtypes. Subtypes in bold show significantly poorer outcome than luminal A subtypes. ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; PR, progesterone receptor.