title: Prognostic factors of survival time after hematopoietic stem cell transplant in acute lymphoblastic leukemia patients: Cox proportional hazard versus accelerated failure time models.
abstract: BACKGROUND
  The aim of this study is to evaluate the prognostic factors of overall survival (OS) after haematopoietic stem cell transplant (HSCT) in acute lymphoblastic leukaemia (ALL) patients using accelerated failure time (AFT), Cox proportional hazard (PH), and Cox time-varying coefficient models.
  
  
  METHODS
  206 patients were enrolled after HSCH in Shariati Hospital between 1993 and 2007. There was evidence of marked departures from the proportional hazards assumption with two prognostic factors, relapse and chronic graft-versus-host disease (cGVHD) (P < .001). Performance among AFT and Cox's models was assessed using explained variation and goodness of fit methods. Discrimination among the exponential, Weibull, generalized gamma (GG), log-logistic, and lognormal distributions was done using maximum likelihood and Akaike information criteria.
  
  
  RESULTS
  The 5-year OS was 52% (95%CI: 47.3-56.7). Peak mortality hazard occurred at months 6-7 after HSCT followed by a decreasing trend. In univariate analysis, the data was better fitted by GG distribution than by other distributions. Univariate analysis using GG distribution showed a positive association between OS with acute graft-versus-host disease (aGVHD) (P = .021), no relapse (P < .001), cGVHD (P < .001), neutrophil recovery (P < .001) and platelet recovery (P < .001). Based on Cox PH models; however cGVHD and relapse were the predictive factors of OS (P < .001). Multivariate analysis indicated that, OS is related to relapse (P < .001) and platelet recovery (P = .037), where predictive power of Weibull AFT models was superior to Cox PH model and Cox with time-varying coefficient (R2 = 0.46 for AFT, R2 = .21 for Cox PH and R2 = .34 for Cox time-varying coefficient). Cox-Snell residual shows Weibull AFT fitted to data better than other distributions in multivariate analysis.
  
  
  CONCLUSIONS
  We concluded that AFT distributions can be a useful tool for recognizing prognostic factors of OS in acute lymphoblastic leukemia patients.
authors.affiliation: Department of Biostatistics, School of Public Health, Tehran University of Medical Sciences, Iran. sayehmiri@razi.tums.ac.ir
authors.forename: Kourosh
authors.initials: K
authors.lastname: Sayehmiri
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Eshraghian
authors.forename: Kazem
authors.initials: K
authors.lastname: Mohammad
authors.forename: Kamran
authors.initials: K
authors.lastname: Alimoghaddam
authors.forename: Abbas Rahimi
authors.initials: AR
authors.lastname: Foroushani
authors.forename: Hojjat
authors.initials: H
authors.lastname: Zeraati
authors.forename: Banafsheh
authors.initials: B
authors.lastname: Golestan
authors.forename: Ardeshir
authors.initials: A
authors.lastname: Ghavamzadeh
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D018380:Hematopoietic Stem Cell Transplantation / Q000401:mortality* / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000401:mortality*; D011379:Prognosis; D016016:Proportional Hazards Models; D019172:Transplantation Conditioning / Q000401:mortality / Q000706:statistics & numerical data; D055815:Young Adult