For localized or bulky disease within the chest, surgery may play a role in debulking the disease. Rituximab has become an effective agent for CD20-positive B cell tumor cells. It has been proposed as a first-line agent against PTLD. This murine/human monoclonal antibody blocks steps in cell cycle progression and differentiation, through complement and antibody-mediated cytotoxicity. Another therapy targeting B cell lymphoma cells is bortezomib, a boron-based drug that causes proteasome inhibition. Chemotherapy may be required for patients with disseminated disease, clinical progression on rituximab, or non-B cell PTLD.