CDK4 and retinoblastoma: Given the strong biologic rationale and supporting preclinical data for evaluating CDK4/6 inhibition in patients with oligodendroglioma,8,10,18 a previous phase 2 clinical trial evaluated palbociclib, the first selective CDK4/6 inhibitor to receive FDA approval, in patients with recurrent retinoblastoma-positive anaplastic oligodendroglioma (AO).25 In that study, Sepulveda-Sanchez et al. enrolled 34 patients with AO that had progressed despite prior RT and chemotherapy and who had conserved retinoblastoma protein (pRb) expression in the tumor by immunohistochemistry.