Heterogeneity of cell lineages in L3 leukemias

Five cases of adult leukemia with L3 morphology in bone marrow were studied for the presence of immunologic, metabolic, and enzymatic markers. Among the five patients, there were four males and female. Median age was 66 with a range of 16-80 yr. Median survival was only 5 mo. Serum lactate dehydrogenase (LDH) levels, 3H-thymidine labeling indices, and DNA/RNA content of the L3 lymphoblasts were markedly elevated. B-cell markers were found in three cases, two exhibiting surface membrane IgM-lambda, and one IgG-K. Terminal deoxynucleotidyl transferase (TdT) enzymatic activity was consistently low in this group. In one case, the L3 lymphoblasts displayed only surface Fc receptors demonstrated by the binding of aggregated IgG. TdT activity was found to be significantly increased. In another instance, the lymphoblasts formed spontaneous rosettes with sheep erythrocytes and exhibited paranuclear staining with acid phosphatase. TdT activity was found to be low. Although most of the L3 leukemias are neoplasias of B lymphocytes, other lineages may also express this morphology.