The NATALEE trial [8] evaluated the addition of ribociclib (400 mg/day, administered on days 1-21 of each 28-day cycle) for three years to adjuvant ET in women with HR-positive, HER2-negative breast cancer, classified as stage II (either N0 with grade 2/3 histology and/or Ki-67 ≥20% or N1) or stage III, according to the eighth edition of the AJCC staging system [6]. This evidence concerns the gene MKI67 and breast carcinoma.