However, 10–40% of HR+/HER2− early-stage BC (EBC) experience metastatic relapse, and HR+/HER2− subtypes such as luminal B (LumB), defined by high tumor grade and high Ki-67 proliferation marker, often have a much poorer response to standard of care treatments [2], hence a higher recurrence rate. This evidence concerns the gene MKI67 and breast cancer.