Clinical and prognostic significance of in vivo differentiation in acute myeloid leukemia
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Bromodeoxyuridine (BrdU) was administered to 86 newly diagnosed patients with standard risk acute myeloid leukemia (AML) prior to starting induction therapy and the labeling index (LI), durations of S-phase (Ts), and the cell cycle (Tc) of myeloblasts were determined. Induction therapy with cytosine arabinoside and daunomycin was subsequently started. Bone marrow biopsies were obtained on days 6 and 17 and weekly thereafter, and were treated with a monoclonal anti-BrdU antibody to determine the fate of cells labeled on day 0 by BrdU. BrdU labeled granulocytes indicating the presence of in vivo differentiation (Diff+) were identified in 48 patients ranging from 1+ (1-10 labeled cells) to 4+ (greater than 31 labeled granulocytes). When compared to 38 differentiation negative (Diff-) patients, Diff+ group had longer Ts (14.5 hr vs. 10.95 hr, P = 0.015) and Tc (59.7 hr vs. 41.7 hr, P = 0.017). Remission duration was significantly longer (no median) for 3-4+ Diff+ as compared to Diff- (median = 220 days) patients (Wilcoxon P = 0.04). We conclude that the detection of in vivo differentiation in AML patients indicates a favorable long-term prognosis either due to the presence of a substantial amount of normal residual hematopoiesis prior to starting induction therapy or due to the ability of leukemic cells to undergo differentiation.
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