Terminal deoxynucleotidyl transferase in the diagnosis of leukemia and malignant lymphoma

Neoplastic cells from 253 patients with leukemia and 46 patients with malignant lymphoma were studied for the presence of terminal deoxynucleotidyl transferase (TdT) by biochemical and fluorescent antibody technics. TdT was detected in circulating blast cells from 73 of 77 patients with acute lymphoblastic leukemia, 24 of 72 patients with chronic myelogenous leukemia examined during the blastic phase of the disorder and in cell suspensions of lymph nodes from nine of nine patients with diffuse lymphoblastic lymphoma. Blast cells from six of 10 patients with acute undifferentiated leukemia were TdT positive, but the enzyme was found in only two of 55 patients with acute myeloblastic leukemia. TdT was not detected in other lymphocytic or granulocytic leukemias or in other types of malignant lymphomas. The fluorescent antibody assay for TdT permits rapid and specific identification of the enzyme in single cells. The TdT assay is clinically useful in confirming the diagnosis of acute lymphoblastic leukemia, evaluating patients with blastic chronic myelogenous leukemia, and distinguishing patients with lymphoblastic lymphoma, whose natural history includes rapid extranodal dissemination, from patients with other poorly differentiated malignant lymphomas.