<qa>  What is the target cancer drug that blocks proteasomes?Rationale: Previous studies testing bortezomib and rituximab separately indicate these agents have some efficacy against mantle cell lymphoma MCL. Bortezomib is a targeted cancer drug that blocks proteasomes. The proteasome is an enzyme complex existing in all cells that influences proteins controlling cellular processes. By blocking the proteasome, bortezomib disrupts biologic pathways such as those related to the growth and survival of cancer cells. Rituximab is a monoclonal antibody that attaches to a protein called the CD20 antigen that is found almost exclusively on the surface of B-cells with leukemia. Once rituximab attaches to the protein, the immune system activates to kill the malignant B-cells. The current study combines bortezomib and rituximab in patients with relapsed or refractory MCL. 