MKI67 and breast cancer: NeoPAL study, in which letrozole plus palbociclib was compared to chemotherapy in the neoadjuvant setting, suggested that the combination of letrozole and palbociclib gave the mean post-treatment Ki-67 of 1.17% in post-treatment samples at the surgery that was performed 24 h after the last dose of palbociclib and might allow sparing chemotherapy in some patients with high-risk luminal breast cancer (34, 35).