Additionally, based on genomic DNA analysis (including copy number, DNA mutations, DNA methylation), gene expression profiling, and protein profiling, phenotypically diverse breast cancers were molecularly characterized and classified into four molecular (intrinsic) groups: luminal A (ER+/PR+/HER2-, low proliferation factor Ki67+ (<14%), low grade), luminal B (ER+/PR±/HER2±, high proliferation factor Ki67+ (≥14%), high grade), HER2-enriched (ER-/PR-/HER2+, any Ki67 level, high proliferation), and basal-like (ER-/PR-/HER2-, any Ki67 level, high grade and proliferation, necrosis) [2,3]. This evidence concerns the gene MKI67 and breast cancer.