Mantle cell lymphoma (MCL) is characterized by cell cycle dysregulation. PD 0332991 is a cyclin-dependent kinase 4 and 6 inhibitor capable of inhibiting cell cycling of MCL. A phase I study has demonstrated the safety and anti-lymphoma activity of PD 0332991. Bortezomib is a first generation proteasome inhibitor approved for treatment of patients with recurrent MCL. Preclinical data suggests that PD 0332991 and bortezomib may act synergistically in MCL.