Terminal transferase in acute lymphoblast leukemia in remission

Terminal deoxynucleotidyl transferase (TdT) is a marker for the diagnosis of acute lymphoblastic leukemia. To determine its value as an indicator of bone marrow remission or impending relapse, serial remission marrows (less than 5% blasts) from 49 patients who had acute lymphoblastic leukemia were examined for TdT by immunofluorescence over the period of a year. Thirty-eight patients (78%) had less than 1% TdT-positive cells. Eleven patients (22%) had slightly elevated levels of TdT (2%-7%) at some time during the study. of these eleven, only two had relapses; however, neither patient had greater than 1% TdT-positive cells within the three months before the relapse. Therefore, it appears that the presence of slightly increased numbers of TdT-positive cells in acute lymphoblastic leukemia remission bone marrows (2%-7%) does not denote impending relapse. In addition, most of the patients with acute lymphoblastic leukemia in remission had less than 1% TdT-positive cells.