Table 1.

Major Subtypes of Human Breast Cancer

Molecular subtype	Gene expression features	Clinical features	Treatment and prognosis
Luminal	Elevated expression of hormone receptors and associated genes (luminal A > luminal B)	~65% of invasive breast cancers are ER- or PR-positive	Respond to endocrine therapy (responses to tamoxifen and aromatase inhibitors may differ in luminal A and B cancers)
		Luminal B cancers tend to be of higher histologic grade than luminal A cancers	Variable response to chemotherapy (greater in luminal B cancers than in luminal A cancers)
		Some overexpress HER2 (luminal B)	Prognosis is better for luminal A cancers than for luminal B cancers
HER2	Elevated expression of HER2 and other genes in amplicon	~15% of invasive breast cancers are ER- or PR-negative	Respond to trastuzumab (Herceptin)
			Respond to anthracycline-based chemotherapy
	Low expression of ER, PR, and associated genes	High probability of being highgrade and node-positive	Prognosis is typically poor
Basallike	Elevated expression of basal epithelial genes and basal cytokeratins	~15% of invasive breast cancers	No response to endocrine therapy or trastuzumab (Herceptin)
	Low expression of ER, PR, and associated genes	Most are ER-, PR-, and HER2- negative (TNBC)	Appear to be sensitive to platinum-based chemotherapy and polyadenosine ribose polymerase inhibitors
	Low expression of HER2	BRCA1 dysfunction (germ line, sporadic)	Prognosis is typically poor (but not uniformly poor)
		Particularly common in African American women

Adapted with permission of (10).