To a large extent, growth inhibition in vivo as in vitro was mediated by Volasertib-triggered cell apoptosis, as demonstrated by higher TUNEL staining and lower Ki-67 staining in comparison with the vehicle control group, especially in the PDX-2 line derived from the patient with recurrent osteosarcoma amputation (Fig. 6J). This evidence concerns the gene MKI67 and osteosarcoma.