Use of terminal deoxynucleotidyl transferase in the diagnosis of leukemia.

Terminal deoxynucleotidyl transferase (TdT) was determined by immunofluorescence in 30 patients with leukemia. In acute lymphocytic leukemia the proportion of cells positive for TdT was 19 to 77 percent during relapse (12 cases) and less than one percent during remission (three cases). In seven cases of myeloproliferative disease and two cases of lymphoma, the TdT was less than one percent. In one case of generalized lymphoblastic lymphoma and five cases of chronic myelocytic leukemia with "lymphoblastic" crisis, the cells positive for TdT were moderately increased. The presence of TdT in blast cells appears to have diagnostic, therapeutic, and prognostic significance.