Purpose: Gemtuzumab ozogamicin (GO), a calicheamicinconjugated mAb against CD33, has been used in the treatment of acute myeloid leukemia (AML). We evaluated the impact of the addition of GO to standard chemotherapy and hematopoietic stem cell transplant (HCT) in patients with FLT3/ITD. Experimental Design: We analyzed children with FLT3/ITD- positive AML (n = 183) treated on two consecutive Children's Oncology GroupAMLtrials (NCT00070174 and NCT00372593). Outcomes were assessed for FLT3/ITD patients receiving standard chemotherapy with or withoutGO(GO vs. No-GO, respectively), and the impact of consolidation HCT for high-risk FLT3/ITD patients [high FLT3/ITD allelic ratio (ITD-AR)]. Results: For all FLT3/ITD patients, complete remission (CR) rates for the GO versus No-GO cohorts were identical (64% vs. 64%; P = 0.98). Relapse rate (RR) after initial CR was 37% for GO recipients versus 59% for No-GO recipients (P = 0.02), disease-free survival (DFS) was similar (47% vs. 41%; P = 0.45), with higher treatment-related mortality (TRM) in GO recipients (16% vs. 0%; P = 0.008). Among high-risk FLT3/ITD patients with high ITD-AR, those who received HCT in first CR with prior exposure to GO had a significant reduction in RR (15% vs. 53%; P = 0.007), with a corresponding DFS of 65% versus 40% (P = 0.08), and higher TRM (19% vs. 7%; P = 0.08). Conclusions: CD33 targeting with HCT consolidation may be an important therapeutic strategy in high-risk FLT3/ITD AML and its efficacy and associated toxicity warrant further investigation.
Bibliographical noteFunding Information:
This work was supported by grants to the Children's Oncology Group including U10 CA98543 (Chair's grant) and U10 CA98413 (Statistical Center). K. Tarlock is an Alex's Lemonade Stand Foundation Young Investigator. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.