CDK 4/6 inhibitors are associated with a high incidence of thrombotic events in women with breast cancer in real-world practice.

VTE in our analysis is higher than reported in clinical trials and arterial thrombosis comprised over one-third of events. The highest incidence was with palbociclib, followed by ribociclib. Khorana score did not predict VTE risk. Larger, real-world studies are needed. The role for prophylactic anticoagulation is yet to be defined in this patient population.