A recent study detected that all luminal A-type cases and most grade 1 luminal B (HER2-positive)-type cases have low proliferative activity (low Ki-67), whereas histological grade is not informative enough to estimate tumour proliferation (Ki-67 expression levels) in luminal B (HER2-negative), HER2 and TNBC cases19. The gene discussed is MKI67; the disease is neoplasm.