A national study from the Korean Breast Cancer Society analyzed the clinical significance of HER2-low expression in early breast cancer and discovered that HER2-low breast cancer exhibited a notable association with a decreased incidence of G3 tumors, diminished Ki-67 labeling index, and fewer TP53 mutations in comparison to HER2-negative (IHC 0) breast cancer (15). This evidence concerns the gene MKI67 and breast cancer.