We did not observe tumor response to palbociclib with the xenograft CD39 (p = 0.40) (which did not harbor a loss of CDKN2A/2B); such an observation raises the possibility to consider CDKN2A/2B loss as a theranostic marker of palbociclib antitumor efficacy in chordomas. This evidence concerns the gene CDKN2A and chordoma.