Terminal deoxynucleotidyl transferase in the blastic phase of chronic myelogenous leukemia: an indicator of response to vincristine and prednisone therapy.

Terminal deoxynucleotidyl transferase (TdT) activity was assayed in leukemic cells of 34 patients in blastic phase of Philadelphia-positive chronic myelogenous leukemia (CML). The TdT levels were correlated with the response to vincristine and prednisone therapy. None of 20 Tdt-negative patients, but 10 of 14 TdT-positive patients responded to vincristine and prednisone. There was poor correlation between blast cell morphology and response to this therapy. This study confirms that TdT levels in the majority of patients predict effectiveness of vincristine and prednisone therapy in blastic phase of CML.