Table 1.

Surrogate definitions of intrinsic subtypes of BC [10, 12]

Intrinsic subtype	Immunohistochemical phenotype	Frequency (%)
Luminal A-like	High ER and PgR; HER2-negative; low proliferation rates; typically low grade; low Ki-67 index	60–70%
Luminal B-like HER2-negative	ER-positive, but ER and PgR expression lower than in luminal A-like; HER2-negative; higher grade; high Ki-67 index	10–20%
Luminal B-like HER2-positive	ER-positive, but ER and PgR expression lower than in luminal A-like; HER2-positive; higher grade; high Ki-67 index	Both 13–15%
HER2-positive (non-luminal)	HER2-positive; ER and PgR absent; high grade; high Ki-67 index
TNBC	ER and PgR absent, HER2-negative; higher grade; high Ki-67 index	10–15%

ER: estrogen receptor; HER2: human epidermal growth factor receptor 2; PgR: progesterone receptor; BC: breast cancer; TNBC: triple-negative breast cancer