Gallen Consensus Meeting [8] determined that the Ki67 labeling index is important for distinguishing between ‘‘luminal A” and ‘‘luminal B (HER2-negative)” breast cancer subtypes, and advised adjuvant chemotherapy for luminal B but not for luminal A. Misinterpretation of the Ki67 labeling index may result in a lost opportunity for patients to receive chemotherapy or may result in patients being overtreated. This evidence concerns the gene ERBB2 and breast cancer.