ORIGINAL ARTICLE A comparison of the outcomes of children with acute myelogenous leukemia in either first or second complete remission (CR1 vs CR2) following allogeneic hematopoietic stem cell transplantation at a single transplant center A Gassas 1 , M Kashif Ishaqi 1 , S Afzal 1 , T Finkelstein-Shechter 1 , A Dupuis 2 and J Doyle 1 1 Division of Haematology/Oncology, Hospital for Sick Children, University of Toronto, Ontario, Canada and 2 Division of Clinical Research Support Unit, Hospital for Sick Children, University of Toronto, Ontario, Canada We reviewed 70 consecutive children with AML who received hematopoietic stem cell transplantation (HSCT) in our institution between 1994 and 2005. Forty-seven children were transplanted in CR1 and 23 were trans- planted in CR2. BU/CY was the most common pre- transplant conditioning regimen for CR1 patients and a TBI-based conditioning regimen was the most common regimen for CR2 patients. Most patients transplanted in CR1 (81%) received related donor HSCT, whereas most of the CR2 patients (74%) received unrelated donor HSCT. Expectedly, there was a significant increase in acute GVHD incidence in CR2 patients (40 vs 25% for grades I–II and 30 vs 10% for grades III–IV; P ¼ 0.02) and a significant increase in transplant-related mortality (38 vs 11%; P ¼ 0.01). Although the difference between 3-year EFS for CR1 and CR2 was not statistically significant, there was a significantly superior 3-year overall survival for CR1 patients (74 vs 51%; P ¼ 0.05). Children with relapsed AML who achieve and maintain remission until HSCT, have a reasonable survival, but the outcome of children receiving HSCT in CR1 remains superior. Bone Marrow Transplantation (2008) 41, 941–945; doi:10.1038/bmt.2008.16; published online 11 February 2008 Keywords: AML; CR1; CR2; hematopoietic stem cell transplantation; children Introduction Significant advances have been made in the treatment of pediatric AML and CR can now be achieved in 490% of children. However, 40–50% of patients relapse after achieving a CR1 with chemotherapy alone, and EFS remains at approximately 50% in most large series. 1–3 Although CR2 may be achieved in the majority of these children with chemotherapy alone, long-term survival is limited to 8–33%. 4–6 While most would recommend allogeneic hematopoietic stem cell transplant (HSCT) as therapy for relapsed AML, the role of HSCT is less certain for children with AML in CR1. 1,2,7 With the excellent results of chemotherapy and the known risks and long-term side effects of HSCT, the decision to proceed with HSCT in CR1 remains controversial. HSCT provides the ability to administer high doses of chemo- or radiotherapy to eradicate the leukemia and the potential benefit of a GVL effect. 8 Survival rates as high as 72% have been reported for children transplanted in CR1. 9 For children with AML beyond CR1, HSCT may be the only curative option. However, the clinical outcome for children transplanted in CR2 is not well defined, as studies published to date report data of these patients combined with other childhood diseases or with adult patients. 10,11 The objective of this study was to determine the outcome of consecutive children with AML who received an allogeneic HSCT in CR2, to compare it with those who received HSCT in CR1 and to analyze the effectiveness of HSCT for this group of patients. Patients, materials and methods We retrospectively reviewed 70 consecutive pediatric patients with AML who underwent first allogeneic HSCT between 1994 and 2005. Patients with mixed-lineage/ biphenotypic acute leukemia and children with Down’s syndrome were excluded. AML subtypes were classified using the FAB system. Risk definition and cytogenetic abnormalities were classified according to the United Kingdom Medical Research Council (UK-MRC) criteria, favorable if t(8;21), t(15;17) or inversion 16 was present, unfavorable if 5, 7, del (5q), abn (3q) and complex cytogenetics and standard group for the remaining. Patient characteristics are described in Table 1. The indications for HSCT in CR1 have changed over the years and as our understanding of childhood AML has progressed. In the early years of the study (1994–1998), Received 22 June 2007; revised 18 December 2007; accepted 24 December 2007; published online 11 February 2008 Correspondence: Dr A Gassas, Division of Hematology/Oncology, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8. E-mail: adam.gassas@sickkids.ca Bone Marrow Transplantation (2008) 41, 941–945 & 2008 Nature Publishing Group All rights reserved 0268-3369/08 $30.00 www.nature.com/bmt