Malignant lymphoma, lymphoblastic.

Among the malignant lymphomas of the diffuse, poorly differentiated lymphocytic type, a cytologically distinctive form can be recognized. It is composed of immature lymphoid cells that are indistinguishable from the cells of acute lymphoblastic leukemia (ALL). Although these neoplasms usually have been classified as malignant lymphoma, lymphoblastic type, they contain, in addition to lymphoblasts, prolymphocytes in varying proportions. On the basis of the nuclear morphology, malignant lymphoma of the lymphoblastic type, (MLLB) can be further divided into those with and those without convoluted nuclei. In our series both groups had the following clinical features in common: 1) frequent occurrence in children and adolescents; 2) clinical presentation with mediastinal masses in 50% of cases; 3) a high incidence of bone marrow and perpheral blood involvement during the course of the disease; and 4) rapid progression of the disease with a median survival of 8 months. Our observations indicate that nuclear convolutions are helpful but not essential for the recognition of a clinicopathologic entity which is histologically and cytologically characterized by 1) the immaturity of the lymphoid cells indistinguishable from the lymphoblasts and prolymphocytes of ALL and 2) a high mitotic index. Because of the frequency with which MLLB progresses into ALL, systemic therapy may be indicated even before this progression is hematologically evident. This indicates the need for morphologic recognition of this malignant lymphoma regardless of the presence of nuclear convolution, age of the patient, and site of presentation.