CNS Involvement in Primary Mediastinal Large B-Cell Lymphoma

The risk of CNS involvement by non-Hodgkin's Lymphoma (NHL) has been associated with bone marrow and/or testicular involvement; however, it was recently reported that the number of extranodal sites is a more reliable predictor of CNS disease. Because primary mediastinal thymic large B-cell lymphoma (PMLCL) has a high propensity for involving extranodal sites, we investigated the frequency and pattern of CNS involvement in PMLCL. The medical records of 219 patients with aggressive NHL, consecutively entered onto protocols at the National Cancer Institute between 1987 and 1998, were retrospectively reviewed. Twenty-three patients (11%) had clinical and pathologic features of PMLCL. These patients were young (median age, 29 years), female (61%), and presented with massive mediastinal adenopathy (70%). Extranodal disease occurred at presentation in 70% and at relapse in 93% of patients and involved contiguous intrathoracic structures and/or distant sites, including the lungs, kidneys, liver, adrenals, ovaries, pancreas, and bone. Six patients (26%) developed CNS involvement, two (9%) at presentation and four (27%) at relapse. All had extranodal disease, but only one had bone marrow involvement. Parenchymal and leptomeningeal CNS disease occurred in four and three patients, respectively. CNS involvement in PMLCL is associated with extranodal involvement other than bone marrow and may reflect the unique biology of this disease. The propensity to involve the CNS parenchyma raises the concern that intrathecal prophylaxis may not be effective and suggests that CNS imaging should be considered in patients with extranodal disease.