Diffuse large B cell lymphoma (DLBCL) is the most common form of non Hodgkin lymphoma, with an annual incidence of 25,000 in the United States and nearly 10,000 deaths per year attributable to the disease. Although chemotherapy is the mainstay of therapy, there has been no improvement in the chemotherapy regimens used to treat DLBCL in the past 30 years. The addition of rituximab to standard chemotherapy has been a significant advance in the treatment of the disease. However, only about 50% of patients with this disease are cured after treatment with chemotherapy and rituximab. There have been over 60 clinical trials in patients with DLBCL that have demonstrated no benefit. An important reason for the failure of many clinical trials in DLBCL may be the approach to the disease as a single entity, even though it is known to be molecularly heterogeneous. Gene expression profiling of patients with DLBCL demonstrated that the tumors comprised at least two distinct diseases with different cells of origin, distinct cytogenetic differences and different response rates to anthracycline-based chemotherapy regimens. In this proposal, we demonstrate how the molecular subclassification of DLBCL reveals new tumor-susceptibilities that can be explored in the clinic.