Significance of Mediastinal Mass in Acute Lymphoblastic Leukemia

A mediastinal mass (MM) is found at the time of diagnosis in 10% to 15% of children with acute lymphoblastic leukemia (ALL).1 In view of the frequent progression of childhood mediastinal lymphoblastic lymphoma (MLL) to leukemia,2,3 ALL + MM may be MLL with early bone marrow involvement. We have found that MLL is a T cell tumor, while ALL is a tumor of cells with neither T nor B cell characteristics.4 Therefore, if ALL + MM is a leukemic stage of MLL, patients with ALL + MM and ALL may differ in their clinical characteristics and responses to therapy. To test this hypothesis, we conducted a retrospective study to compare children with ALL + MM and ALL followed in this clinic over the last seven years.