Phase II Palbociclib +Ibrutinib in Mantle Cell Lymphoma

Treatment will consist of: * Palbociclib administered at 100 mg oral once daily for 21 days on followed by 7 days off * Ibrutinib administered at 560 mg oral continuously Patients will continue to receive study drugs until disease progression, unacceptable toxicity, or withdrawal of consent. If at any time one of the agents is held due to toxicity, the other agent may be continued in those patients who are receiving clinical benefit. Response will be assessed by PET/CT and/or CT every 3 cycles while on therapy for the first year and then every 6 cycles thereafter until disease progression or at the investigator's discretion if otherwise medically indicated. A PET will be required to confirm CR. A bone marrow biopsy will be performed in patients with bone marrow involvement at the start of therapy to confirm complete response once patients have otherwise met criteria for CR.