Table 1.

Immunohistochemical staining for the intrinsic breast cancer molecular subtypes*

IHC subtype (%)†	ER and/or PR	HER2	Ki67	Intrinsic subtype
Luminal A (73%)	Positive	Negative	Low	Luminal A
Luminal B (10%)	Positive	Negative or positive	Low or high	Luminal B
HER2 positive, nonluminal (5%)	Negative	Positive	Not needed	HER2-enriched
Triple-negative (12%)	Negative	Negative	Not needed	Basal-like

* There are two predominantly hormone-positive (estrogen receptor [ER] and/or progesterone receptor [PR]) intrinsic molecular subtypes (luminal A and luminal B) and two predominantly hormone-negative intrinsic subtypes (human epidermal growth factor receptor 2 [HER2] enriched and basal-like) (133–136). Additionally, there are two predominantly HER2-positive intrinsic molecular subtypes (luminal B and HER2 enriched) and two predominantly HER2-negative intrinsic subtypes (luminal A and Basal-like). Adapted from Goldhirsch et al. (157). IHC = immunohistochemical.

† Estimated percentage distribution for IHC-derived subtypes among women with breast cancer and known ER, PR, and HER2 expression in the general population of the United States in 2010, provided by the National Cancer Institute’s SEER database (178).