Flavopiridol to Treat Relapsed Mantle Cell Lymphoma or Diffuse Large B-Cell Lymphoma

Background: Mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL) are aggressive subtypes of non-Hodgkin lymphoma. Flavopiridol is an investigational drug that works differently from standard chemotherapy and may target abnormalities in MCL and DLBCL cells, such as a protein excess that prevents tumor cells from dying. A challenge in developing flavopiridol for treatment has been determining its optimal dosing schedule. The schedule used for this study is effective in a type of leukemia called chronic lymphocytic leukemia (CLL) and may benefit patients with MCL and DLBCL also. Objectives: To determine the highest dose of flavopiridol that can be given safely to patients with relapsed MCL and DLBCL at the dosing schedule detailed below To assess the response of the tumor to flavopiridol given at the test dosing schedule Eligibility: Patients 18 years of age and older with relapsed MCL or DLBCL Design: Flavopiridol is given at four different dose levels, starting with the lowest dose for the first group of three to six patients and increasing with subsequent groups, depending on side effects at the preceding dose. The drug is given weekly for 4 weeks followed by a 2-week break (one cycle) for up to six cycles. It is given through a vein as a 30-minute infusion followed by a 4-hour infusion. Patients undergo the following procedures for research studies and to evaluate the effect of treatment on the tumor: * Blood tests * Lymph node, bone marrow and tumor biopsies * Lymphapheresis to collect blood cells for research * Disease staging with imaging studies (computed tomography (CT), positron emission tomography (PET) and/or magnetic resonance imaging (MRI) after every 2 cycles