Based on these receptor pathways, breast cancers are classified into four subtypes—luminal A (ER+ and/or PR+, HER2−, Ki-67 < 14 %), luminal B (ER+ and/or PR+, HER2−, Ki-67 ≥ 14 % or ER+ and/or PR+, HR2+), HER2-enriched (ER−, PR−, HER2+), and triple-negative breast cancer (TNBC) (ER−, PR−, HER2−). The gene discussed is MKI67; the disease is breast cancer.