Koh et al. Journal of Experimental & Clinical Cancer Research 2011, 30:36 http://www.jeccr.com/content/30/1/36 Page 2 of 7 Introduction Patients with primary refractory or refractory relapsed acute leukemia have an extremely poor prognosis. It has been generally recognized that few cases with primary refractory or refractory relapsed acute leukemia can be cured using conventional chemotherapy alone [1]. While allogeneic hematopoietic cell transplantation (allo-HCT) has the potential to cure even active leukemia, it has not been determined what subgroup can receive a long-term benefit from it. Several retrospective studies have reported the prog- nostic factors for allo-HCT in patients not in remission at allo-HCT including untreated first relapse cases [2-8]. However, the factors contributing to long-term survival have not been established because the follow-up periods of these studies were not long enough at less than five years. Importantly, it can be assumed that patients who survive for more than five years without leukemia relapse are most likely cured. Only one large-scale retro- spective study has examined long-term outcomes for more than five years following allo-HCT in adult patients with acute leukemia not in remission [9]. This study showed that several pre-transplant variables including complete remission duration, type of donor, disease burden, performance status, age and cytogenetics affected survival. However, whether post-transplant vari- ables such as acute or chronic graft-versus-host disease (GVHD) influenced the post-HCT prognosis was not assessed. To our knowledge, no studies have investigated pre- and/or post-transplant factors which are associated with long-term survival exclusively in adult patients with active leukemia at allo-HCT. Therefore, we com- prehensively evaluated the pre- and post-transplant fac- tors which contribute to long-term survival of more than five years in patients with leukemia not in remis- sion at allo-HCT. Patients and methods Between January 1999 and July 2009, 42 consecutive patients (24 males and 18 females) with leukemia not in remission, aged 15 to 67 years (median age: 39 years), underwent allo-HCT at our institution. Patients with de novo acute myeloid leukemia (AML; n = 17), acute lym- phoblastic leukemia (ALL; n = 12), chronic myeloid leu- kemia in accelerated phase (CML-AP; n = 2), myelodysplastic syndrome (MDS) overt AML (n = 10) and plasma cell leukemia (n = 1) were included. High- risk AML was defined according to the Eastern Coop- erative Oncology Group/Southwest Oncology Group classification as having poor-risk cytogenetics (5/del[5q], 7/del[7q], inv[3q], abn11q, 20q or 21q, del[9q], t[6;9], t [9;22], abn17p, and complex karyotype defined as three or more abnormalities) [10]. High-risk ALL was defined as having poor-risk cytogenetics with either t(4:11), t (9;22), t(8;14), hypodiploidy or near triploidy, or more than five cytogenetic abnormalities [11]. Of study sub- jects with acute leukemia, cytogenetic abnormalities were intermediate (n = 17, 44%) or poor (n = 22, 56%). Seven patients were primary refractory to induction che- motherapy. The other patients relapsed after conven- tional chemotherapy (n = 23) or the first or the second HCT (n = 9). The median number of blast cells in bone marrow (BM) was 26.0% (range; 0.2-100) before the start of chemotherapy for allo-HCT. Six patients had leukemic involvement of the central nervous system (CNS). Stem cell sources were related BM (n = 3, 7%), related peripheral blood (PB) (n = 13, 31%), unrelated BM (n = 20, 48%) and unrelated cord blood (CB) (n = 6, 14%). Standard serologic typing was used for human leukocyte antigen (HLA) -A, B and DRB1. Thirty-one pairs were matched for HLA-A, B and DRB1 antigens. Three patients were mismatched for one HLA antigen (two at HLA-A, one at HLA-B), and seven were mis- matched for two (two at HLA-A and B, five (all CB) at HLA-B and DRB1). The remaining one patient was mis- matched for all three antigens (haploidentical). We clas- sified conditioning regimens into four categories. Standard conditioning (n = 12) comprised a busulfan- based or total body irradiation (TBI)-based (12Gy) regi- men. Busulfan was given as a total of 16 mg/kg orally or equivalent dose, 12.8 mg/kg intravenously (i.v.). Intensi- fied conditioning (n = 9) consisted of additional cytore- ductive chemotherapy in the three weeks before conditioning, followed by standard conditioning. Of the 21 patients receiving standard or intensified condition- ing, 13 patients received the TBI-based regimen. Reduced-intensity conditioning (n = 21) comprised a fludarabine-based (n = 20) and cladribine-based regimen (n = 1). Fludarabine was given as 25-35 mg/m2 i.v. on five or six consecutive days. Of the 21 patients receiving reduced-intensity conditioning, 14 patients received cytoreductive chemotherapy in the three weeks before conditioning. Prophylaxis for acute GVHD was a calci- neurin inhibitor alone (n = 5), calcineurin inhibitor plus short-term methotrexate (n = 32), calcineurin inhibitor plus mycophenolate mofetil (n = 2), or none (n = 3). The calcineurin inhibitor included cyclosporine adminis- tered to 33 patients and tacrolimus to six patients. End points The absence of post-transplant remission in some patients biased the calculation of relapse rate, nonre- lapse mortality (NRM) and leukemia-free survival (LFS). Therefore, we set five-year overall survival (OS) as the primary end point. OS was defined as time from the date of last transplantation to the date of death or