CDK4 and malignant peripheral nerve sheath tumor: Our laboratory discovered a new player in MPNST pathogenesis with functional ties to ARF and CDK4/6-RB1 signaling, an oncoprotein named RABL6A (Rab-like GTPase isoform 6A, also called the partner of ARF [PARF], RBEL1, or c9orf86).