In this current study, we explored the antitumor effect of the targeted therapy palbociclib in three PDX chordoma models in order to consider the homozygous deletion of CDKN2A/2B as a theranostic biomarker of response to palbociclib, as suggested in other cancer types (43, 54, 55). The gene discussed is CDKN2A; the disease is cancer.