Table 2.

The biological subtypes of breast cancer.

Subtypes	Estrogen receptor (ER)	Human epidermal growth factor receptor-2 (HER2)	Ki-67 protein	Progesterone receptor (PR)	Comment
Luminal A  Luminal B	Positive  Positive	Negative  Positive or Negative	Low  High	Positive or Negative  Positive or Negative	In comparing luminal A and B, luminal A is reported to be growing slower than luminal B, which means best prognosis in luminal A cancer; Ki-67 helps in monitoring how fast tumours grow.
Triple-negative (basal-like)	Negative	Negative	-	Negative	It is defined as basal-like breast cancer and is more common among young women especially with BRCA1 gene mutations.
HER2-enriched	Negative	Positive	-	Negative	This cancer is growing faster than luminal cancers but with worse prognosis.
Normal-like	Positive	Negative	Low	Positive or Negative	Although ‘normal-like' is similar to luminal A, its prognosis is worse than luminal A.