Terminal transferase as a predictor of initial responsiveness to vincristine and prednisone in blastic chronic myelogenous leukemia: a co-operative study.

We undertook a prospective trial to evaluate terminal deoxynucleotidyl transferase activity as a predictor of responsiveness to vincristine and prednisone in 22 Philadelphia-chromosome-positive patients with blastic chronic myelogenous leukemia. Thirteen patients were transferase positive, and nine negative. None of the nine negative patients responded, whereas eight of the 13 positive (P = 0.004) responded with complete clearing of peripheral blood blast cells and a return of normal marrow cellularity with less than 5 per cent blast cells. Among transferase-positive patients under 50 years of age the response rate was 78 per cent. Blast-cell morphology (i.e., lymphoblastic versus myeloblastic) had no significant correlation with either responsiveness or terminal transferase activity. The results of this study suggest that responsiveness to vincristine and prednisone in blastic chronic myelogenous leukemia is confined to patients whose leukemic cells are transferase positive.