Comparing Outcomes with Bone Marrow or Peripheral Blood Stem Cells as Graft Source for Matched Sibling Transplants in Severe Aplastic Anemia across Different Economic Regions.

Bone marrow (BM) is the preferred graft source for hematopoietic stem cell transplantation (HSCT) in severe aplastic anemia (SAA) compared with mobilized peripheral blood stem cells (PBSCs). We hypothesized that this recommendation may not apply to those regions where patients present later in their disease course, with heavier transfusion load and with higher graft failure rates. Patients with SAA who received HSCT from an HLA-matched sibling donor from 1995 to 2009 and reported to the Center for International Blood and Marrow Transplant Research or the Japan Society for Hematopoietic Cell Transplantation were analyzed. The study population was categorized by gross national income per capita and region/countries into 4 groups. Groups analyzed were high-income countries (HIC), which were further divided into United States-Canada (n = 486) and other HIC (n = 1264); upper middle income (UMIC) (n = 482); and combined lower-middle, low-income countries (LM-LIC) (n = 142). In multivariate analysis, overall survival (OS) was highest with BM as graft source in HIC compared with PBSCs in all countries or BM in UMIC or LM-LIC (P < .001). There was no significant difference in OS between BM and PBSCs in UMIC (P = .32) or LM-LIC (P = .23). In LM-LIC the 28-day neutrophil engraftment was higher with PBSCs compared with BM (97% versus 77%, P = .002). Chronic graft-versus-host disease was significantly higher with PBSCs in all groups. Whereas BM should definitely be the preferred graft source for HLA-matched sibling HSCT in SAA, PBSCs may be an acceptable alternative in countries with limited resources when treating patients at high risk of graft failure and infective complications.

The Impact of Graft-versus-Host Disease on the Relapse Rate in Patients with Lymphoma Depends on the Histological Subtype and the Intensity of the Conditioning Regimen.

The purpose of this study was to analyze the impact of graft-versus-host disease (GVHD) on the relapse rate of different lymphoma subtypes after allogeneic hematopoietic cell transplantation (allo-HCT). Adult patients with a diagnosis of Hodgkin lymphoma, diffuse large B cell lymphoma, follicular lymphoma (FL), peripheral T cell lymphoma, or mantle cell lymphoma (MCL) undergoing HLA-identical sibling or unrelated donor hematopoietic cell transplantation between 1997 and 2009 were included. Two thousand six hundred eleven cases were included. A reduced-intensity conditioning (RIC) regimen was used in 62.8% of the transplantations. In a multivariate analysis of myeloablative cases (n = 970), neither acute (aGVHD) nor chronic GVHD (cGVHD) were significantly associated with a lower incidence of relapse/progression in any lymphoma subtype. In contrast, the analysis of RIC cases (n = 1641) showed that cGVHD was associated with a lower incidence of relapse/progression in FL (risk ratio [RR], .51; P = .049) and in MCL (RR, .41; P = .019). Patients with FL or MCL developing both aGVHD and cGVHD had the lowest risk of relapse (RR, .14; P = .007; and RR, .15; P = .0019, respectively). Of interest, the effect of GVHD on decreasing relapse was similar in patients with sensitive disease and chemoresistant disease. Unfortunately, both aGVHD and cGVHD had a deleterious effect on treatment-related mortality and overall survival (OS) in FL cases but did not affect treatment-related mortality, OS or PFS in MCL. This study reinforces the use of RIC allo-HCT as a platform for immunotherapy in FL and MCL patients.

Impact of Chronic Graft-versus-Host Disease on Late Relapse and Survival on 7,489 Patients after Myeloablative Allogeneic Hematopoietic Cell Transplantation for Leukemia.

PURPOSE: Malignancy relapse remains a major obstacle for successful allogeneic hematopoietic cell transplantation (HCT). Chronic graft-versus-host disease (cGVHD) is associated with fewer relapses. However, when studying effects of cGVHD on relapse, it is difficult to separate from acute GVHD effects as most cases of cGVHD occur within the first year after transplant at the time when acute GVHD is still active. EXPERIMENTAL DESIGN: This study based on CIBMTR registry data investigated cGVHD and its association with the incidence of late relapse and survival in 7,489 patients with acute myelogenous leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML), and myelodysplastic syndromes (MDS), who were leukemia free at 12 months after myeloablative allogeneic HCT. RESULTS: Forty-seven percent of the study population was diagnosed with cGVHD at 12 months after transplant. The protective effect of cGVHD on late relapse was present only in patients with CML [RR, 0.47; 95% confidence interval (CI), 0.37-0.59; P < 0.0001). cGVHD was significantly associated with higher risk of treatment-related mortality (TRM; RR, 2.43; 95% CI, 2.09-2.82; P < 0.0001) and inferior overall survival (RR, 1.56; 95% CI, 1.41-1.73; P < 0.0001) for all diseases. In patients with CML, all organ sites and presentation types of cGVHD were equally associated with lower risk of late relapse. CONCLUSIONS: These results indicate that clinically relevant antileukemia effects of cGVHD on late relapses are present only in CML but not in AML, ALL, or MDS. Chronic GVHD in patients who are 1-year survivors after myeloablative allogeneic HCT is primarily associated with higher TRM and inferior survival.

Center for International Blood and Marrow Transplant Research chronic graft-versus-host disease risk score predicts mortality in an independent validation cohort.

We previously reported a risk score that predicted mortality in patients with chronic graft-versus-host disease (CGVHD) after hematopoietic stem cell transplantation (HCT) between 1995 and 2004 and reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). We sought to validate this risk score in an independent CIBMTR cohort of 1128 patients with CGVHD who underwent transplantation between 2005 and 2007 using the same inclusion criteria and risk score calculations. According to the sum of the overall risk score (range, 1 to 12), patients were assigned to 4 risk groups (RGs): RG1 (0 to 2), RG2 (3 to 6), RG3 (7 to 8), and RG4 (9 to 10). RG3 and RG4 were combined, as RG4 accounted for only 1% of the total cohort. Cumulative incidences of nonrelapse mortality (NRM) and probability of overall survival were significantly different between each RG (all P < .01). NRM and overall survival at 5 years after CGVHD for each RG were 17% and 72% in RG1, 26% and 53% in RG2, and 44% and 25% in RG3, respectively (all P < .01). Our study validates the prognostic value of the CIBMTR CGVHD RGs for overall survival and NRM in a contemporary transplantation population. The CIBMTR CGVHD RGs can be used to predict major outcomes, tailor treatment planning, and enroll patients in clinical trials.

Bayesian Transformation Models for Multivariate Survival Data.

In this paper we propose a general class of gamma frailty transformation models for multivariate survival data. The transformation class includes the commonly used proportional hazards and proportional odds models. The proposed class also includes a family of cure rate models. Under an improper prior for the parameters, we establish propriety of the posterior distribution. A novel Gibbs sampling algorithm is developed for sampling from the observed data posterior distribution. A simulation study is conducted to examine the properties of the proposed methodology. An application to a data set from a cord blood transplantation study is also reported.

Donor killer cell Ig-like receptor B haplotypes, recipient HLA-C1, and HLA-C mismatch enhance the clinical benefit of unrelated transplantation for acute myelogenous leukemia.

Killer cell Ig-like receptors (KIRs) interact with HLA class I ligands to regulate NK cell development and function. These interactions affect the outcome of unrelated donor hematopoietic cell transplantation (HCT). We have shown previously that donors with KIR B versus KIR A haplotypes improve the clinical outcome for patients with acute myelogenous leukemia by reducing the incidence of leukemic relapse and improving leukemia-free survival (LFS). Both centromeric and telomeric KIR B genes contribute to the effect, but the centromeric genes are dominant. They include the genes encoding inhibitory KIRs that are specific for the C1 and C2 epitopes of HLA-C. We used an expanded cohort of 1532 T cell-replete transplants to examine the interaction between donor KIR B genes and recipient class I HLA KIR ligands. The relapse protection associated with donor KIR B is enhanced in recipients who have one or two C1-bearing HLA-C allotypes, compared with C2 homozygous recipients, with no effect due to donor HLA. The protective interaction between donors with two or more, versus none or one, KIR B motifs and recipient C1 was specific to transplants with class I mismatch at HLA-C (RR of leukemia-free survival, 0.57 [0.40-0.79]; p = 0.001) irrespective of the KIR ligand mismatch status of the transplant. The survival advantage and relapse protection in C1/x recipients compared with C2/C2 recipients was similar irrespective of the particular donor KIR B genes. Understanding the interactions between donor KIR and recipient HLA class I can be used to inform donor selection to improve outcome of unrelated donor hematopoietic cell transplantation for acute myelogenous leukemia.

Impact of allele-level HLA matching on outcomes after myeloablative single unit umbilical cord blood transplantation for hematologic malignancy.

We studied the effect of allele-level matching at human leukocyte antigen (HLA)-A, -B, -C, and -DRB1 in 1568 single umbilical cord blood (UCB) transplantations for hematologic malignancy. The primary end point was nonrelapse mortality (NRM). Only 7% of units were allele matched at HLA-A, -B, -C, and -DRB1; 15% were mismatched at 1, 26% at 2, 30% at 3, 16% at 4, and 5% at 5 alleles. In a subset, allele-level HLA match was assigned using imputation; concordance between HLA-match assignment and outcome correlation was confirmed between the actual and imputed HLA-match groups. Compared with HLA-matched units, neutrophil recovery was lower with mismatches at 3, 4, or 5, but not 1 or 2 alleles. NRM was higher with units mismatched at 1, 2, 3, 4, or 5 alleles compared with HLA-matched units. The observed effects are independent of cell dose and patient age. These data support allele-level HLA matching in the selection of single UCB units.

Comparison of statistics in association tests of genetic markers for survival outcomes.

Computationally efficient statistical tests are needed in association testing of large scale genetic markers for survival outcomes. In this study, we explore several test statistics based on the Cox proportional hazards model for survival data. First, we consider the classical partial likelihood-based Wald and score tests. A revised way to compute the score statistics is explored to improve the computational efficiency. Next, we propose a Cox-Snell residual-based score test, which allows us to handle the controlling variables more conveniently. We also illustrated the incorporation of these three tests into a permutation procedure to adjust for the multiple testing. In addition, we examine a simulation-based approach proposed by Lin (2005) to adjust for multiple testing. We presented the comparison of these four statistics in terms of type I error, power, family-wise error rate, and computational efficiency under various scenarios via extensive simulation.

Multiple mismatches at the low expression HLA loci DP, DQ, and DRB3/4/5 associate with adverse outcomes in hematopoietic stem cell transplantation.

A single mismatch in highly expressed HLA-A, -B, -C, and -DRB1 loci (HEL) is associated with worse outcomes in hematopoietic stem cell transplantation, while less is known about the cumulative impact of mismatches in the lesser expressed HLA loci DRB3/4/5, DQ, and DP (LEL). We studied whether accumulation of LEL mismatches is associated with deleterious effects in 3853 unrelated donor transplants stratified according to number of matches in the HEL. In the 8/8 matched HEL group, LEL mismatches were not associated with any adverse outcome. Mismatches at HLA-DRB1 were associated with occurrence of multiple LEL mismatches. In the 7/8 HEL group, patients with 3 or more LEL mismatches scored in the graft-versus-host vector had a significantly higher risk of mortality (1.45 and 1.43) and transplant-related mortality (1.68 and 1.54) than the subgroups with 0 or 1 LEL mismatches. No single LEL locus had a more pronounced effect on clinical outcome. Three or more LEL mismatches are associated with lower survival after 7/8 HEL matched transplantation. Prospective evaluation of matching for HLA-DRB3/4/5, -DQ, and -DP loci is warranted to reduce posttransplant risks in donor-recipient pairs matched for 7/8 HEL.

Recipient survival and graft survival are not diminished by simultaneous liver-kidney transplantation: an analysis of the united network for organ sharing database.

Recipients of solitary liver and kidney transplants are living longer, and this increases their risk of long-term complications such as recurrent hepatitis C virus (HCV) and drug-induced nephrotoxicity. These complications may require retransplantation. Since the adoption of the Model for End-Stage Liver Disease, the number of simultaneous liver-kidney transplantation (SLK) procedures has increased. However, there are no standardized criteria for organ allocation to SLK candidates. The aims of this study were to retrospectively compare recipient and graft survival with liver transplantation alone (LTA), SLK, kidney after liver transplantation (KALT), and liver after kidney transplantation (LAKT) and to identify independent risk factors affecting recipient and graft survival. The United Network for Organ Sharing/Organ Procurement and Transplantation Network database (1988-2007) was queried for adult LTA (66,026), SLK (2327), KALT (1738), and LAKT procedures (242). After adjustments for potential confounding demographic and clinical variables, there was no difference in recipient mortality rates with LTA and SLK (P = 0.02). However, there was a 15% decreased risk of graft loss with SLK versus LTA (hazard ratio = 0.85, P < 0.001). The recipient and graft survival rates with SLK were higher than the rates with both KALT (P <0.001 and P <0.001) and LAKT (P = 0.003 and P < 0.001). The following were all identified as independent negative predictors of recipient mortality and graft loss: recipient age ≥ 65 years, male sex, black race, HCV/diabetes mellitus status, donor age ≥ 60 years, serum creatinine level ≥2.0 mg/dL, cold ischemia time > 12 hours, and warm ischemia time > 60 minutes. Although the recent increase in the number of SLK procedures performed each year has effectively decreased the number of potential donor kidneys available to patients with end-stage renal disease (ESRD) awaiting kidney transplantation, SLK in patients with end-stage liver disease and ESRD is justified because of the lower risk of graft loss with SLK versus LTA as well as the superior recipient and graft survival with SLK versus serial liver-kidney transplantation.

Analysis of non-HLA genomic risk factors in HLA-matched unrelated donor hematopoietic cell transplantation for chronic myeloid leukemia.

BACKGROUND: Allogeneic hematopoietic cell transplantation is the main curative therapy for patients with chronic myeloid leukemia who do not respond to tyrosine kinase inhibitors. It has been proposed that non-human leukocyte antigen gene polymorphisms influence outcome after hematopoietic cell transplantation and could be used alongside traditional patient-donor and transplant characteristics to create a recipient risk profile associated with allogeneic hematopoietic cell transplantation. DESIGN AND METHODS: A previous study from the European Group for Blood and Marrow Transplantation showed that the absence of recipient tumor necrosis factor receptor II, absence of donor interleukin 10 ATA/ACC and presence of donor interleukin 1 receptor antagonist allele 2 genotypes were associated with decreased survival and increased non-relapse mortality in adult patients with chronic myeloid leukemia undergoing myeloablative human leukocyte antigen-identical sibling transplantation. To explore these associations in unrelated donor transplantation, these polymorphisms were genotyped in 383 adult patients with chronic myeloid leukemia who underwent hematopoietic cell transplantation from unrelated donors matched for 10/10 human leukocyte antigens. RESULTS: The polymorphisms were not associated with overall survival, non-relapse mortality, relapse or acute graft-versus-host disease in the unrelated donor cohort. Comparison of the unrelated donor and human leukocyte antigen-identical sibling cohorts showed differences in survival and clinical characteristics. CONCLUSIONS: We did not confirm that non-human leukocyte antigen polymorphisms were associated with outcomes in myeloablative unrelated donor hematopoietic cell transplantation for chronic myeloid leukemia, possibly because of the strong association between clinical variables and outcome which masked more subtle genetic effects.

Relationship of race/ethnicity and survival after single umbilical cord blood transplantation for adults and children with leukemia and myelodysplastic syndromes.

The relationship of race/ethnicity with outcomes of umbilical cord blood transplantation (UCBT) is not well known. We analyzed the association between race/ethnicity and outcomes of unrelated single UCBT for leukemia and myelodysplastic syndromes. Our retrospective cohort study consisted of 885 adults and children (612 whites, 145 blacks, and 128 Hispanics) who received unrelated single UCBT for leukemia and myelodysplastic syndromes between 1995 and 2006 and were reported to the Center for International Blood and Marrow Transplant Research. A 5-6/6 HLA-matched unit with a total nucleated cell count infused of ≥2.5 × 10(7)/kg was given to 40% white and 42% Hispanic, but only 21% black patients. Overall survival at 2 years was 44% for whites, 34% for blacks, and 46% for Hispanics (P = .008). In multivariate analysis adjusting for patient, disease, and treatment factors (including HLA match and cell dose), blacks had inferior overall survival (relative risk of death, 1.31; P = .02), whereas overall survival of Hispanics was similar (relative risk, 1.03; P = .81) to that of whites. For all patients, younger age, early-stage disease, use of units with higher cell dose, and performance status ≥80 were independent predictors of improved survival. Black patients and white patients infused with well-matched cords had comparable survival; similarly, black and white patients receiving units with adequate cell dose had similar survival. These results suggest that blacks have inferior survival to whites after single UCBT, but outcomes are improved when units with a higher cell dose are used.

Effect of donor-recipient HLA matching at HLA A, B, C, and DRB1 on outcomes after umbilical-cord blood transplantation for leukaemia and myelodysplastic syndrome: a retrospective analysis.

BACKGROUND: The importance of matching at the HLA C locus has not been well defined for unrelated umbilical-cord blood transplantation. The selection algorithm for umbilical-cord blood units generally considers intermediate resolution HLA typing at A and B and allele-level typing at DRB1. We aimed to establish the relative importance of additional matching at HLA C. METHODS: We used Cox regression to assess retrospectively the effect of donor-recipient HLA matching on outcomes of single umbilical-cord blood transplantations for leukaemia and myelodysplastic syndrome. Our primary endpoint was transplant-related mortality. HLA typing was done with molecular techniques with a minimum of intermediate resolution for HLA A, B, and C, and at the allele-level for DRB1. FINDINGS: The median age of our study population was 10 years (range <1-62) and 552 (69%) of 803 patients were aged 16 years or younger at transplantation. Compared with transplantations matched at HLA A, B, C, and DRB1 (n=69), transplant-related mortality risk was higher after transplantations matched at HLA A, B, and DRB1 and mismatched at HLA C (n=23; HR 3·97, 95% CI 1·27-12·40; p=0·018). Transplant-related mortality risk was also higher after transplantations with a single mismatch at HLA A, B, or DRB1 and mismatched at HLA C (n=234; 1·70, 1·06-2·74; p=0·029) compared with transplantations matched at HLA C with a single mismatch at HLA A, B, or DRB1 (n=127). Assessing the overall effect of HLA disparity on transplant-related mortality, risks were higher with units mismatched at two (n=259; 3·27, 1·42-7·54; p=0·006), three (n=253; 3·34, 1·45-7·71; p=0·005), or four (n=75; 3·51, 1·44-8·58; p=0·006) loci compared with matched units (n=69). INTERPRETATION: Our data suggest that the present strategy for umbilical-cord blood unit selection should be reassessed; matching at HLA C for units that are matched at HLA A, B, or DRB1 or in the presence of a single locus mismatch at HLA A, B, or DRB1 should be included to minimise mortality risks. FUNDING: National Cancer Institute, National Heart Lung and Blood Institute, National Institute for Allergy and Infectious Diseases, Leukemia and Lymphoma Society, US Department of the Navy, Children's Leukemia Research Association, and INSERM.

Risk factors associated with increased nonrelapse mortality and with poor overall survival in children with chronic graft-versus-host disease.

There is a paucity of information regarding the factors that affect nonrelapse mortality (NRM) and overall survival among children that develop chronic graft-versus-host disease (cGVHD). We performed multivariate analyses using data from the Center for International Blood and Marrow Transplant Research to identify risk factors for NRM and survival in 1117 pediatric subjects with leukemia or myelodysplastic syndrome, transplanted from related donors, unrelated donors (URD), or unrelated cord blood between 1995 and 2004. We identified 4 variables associated with higher NRM: HLA partially matched or mismatched URD, peripheral blood cell graft, Karnofsky/Lansky score < 80 at cGVHD diagnosis, and platelets < 100 × 10(9)/L at cGVHD diagnosis. Factors associated with significantly worse survival were: age > 10 years, transplantation from HLA partially matched or mismatched URD, advanced disease at transplantation, Karnofsky/Lansky < 80; and platelets < 100 × 10(9)/L. Cumulative incidence of discontinuation of systemic immune suppression at 1, 3, and 5 years after diagnosis of cGVHD were 22% (20%-25%), 34% (31%-37%), and 37% (34%-40%), respectively. This is the largest study elucidating variables affecting outcome after diagnosis of cGVHD in pediatric allograft recipients. These variables may be useful for risk stratification, development of future clinical trials, and family counseling in children with cGVHD.

Chronic GVHD risk score: a Center for International Blood and Marrow Transplant Research analysis.

Several risk factors are associated with increased mortality in patients with chronic graft-versus-host disease (cGVHD), but there is considerable variability in the reported factors. Therefore, we evaluated patient, transplantation, and cGVHD characteristics to develop a risk score in 5343 patients with cGVHD. Ten variables were identified as being significant in multivariate analysis of overall survival and nonrelapse mortality (NRM): age, prior acute GVHD, time from transplantation to cGVHD, donor type, disease status at transplantation, GVHD prophylaxis, gender mismatch, serum bilirubin, Karnofsky score, and platelet count. These 10 variables were used to build a cGVHD risk score, and 6 risk groups (RGs) were identified. The 5-year NRM was 5% (1%-9%) in RG1, 20% (19%-23%) in RG2, 33% (29%-37%) in RG3, 43% (40%-46%) in RG4, 63% (53%-74%) in RG5, and 72% (59%-85%) in RG6. The 5-year overall survival was highest at 91% (95% confidence interval [CI]:85%-97%) in RG1, followed by 67% (65%-69%) in RG2, 51% (46%-55%) in RG3, 40% (37%-43%) in RG4, 21% (12%-30%) in RG5, and 4% (0%-9%) in RG6 (all P < .01). This analysis demonstrates the usefulness of data from a large registry to develop risk-score categories for major transplantation outcomes. Validation of this cGVHD risk score is needed in a different population to ensure its broad applicability.

Frequency and magnitude of interferon ß neutralizing antibodies in the evaluation of interferon ß immunogenicity in patients with multiple sclerosis.

Patients with multiple sclerosis (MS) treated with interferon ß (IFNß) preparations develop varying levels of antibodies that neutralize the biological effects of IFNß, reduce its in vivo bioavailability, and diminish its therapeutic efficacy. The aim was to determine as distinct measures of immunogenicity the occurrence (frequency) and the magnitude (level) of IFNß neutralizing antibody (NAb) formation in a large Canadian population as a cross-sectional study of patients with MS treated in a clinical practice setting with different, equally available IFNß products: Avonex(®) (intramuscular IFNß-1a), Rebif(®) (subcutaneous (SC) IFNß-1a) at 22 and 44 µg, and Betaseron(®) (SC IFNß-1b). Over a 3-year period 3,124 serum samples from 2,711 patients with MS were submitted by neurologists in MS clinics distributed across Canada and tested for NAbs in a single independent laboratory, utilizing a quantitative, standardized NAb bioassay. NAb frequency was greatest (35%) with Rebif (SC IFNß-1a) 44 µg and least (7.5%) with Avonex (intramuscular IFNß-1a), whereas Betaseron (IFNß-1b) and Rebif 22 µg were in between (22%). NAb serum levels at magnitudes considered high, ≥100 tenfold reduction units (TRU)/mL, were found in 65%-83% of patients with detectable NAbs. Nearly half (42%-47%) of NAb-positive patients given IFNß-1a preparations had very high titers (≥ 1,000 TRU/mL), whereas only 22% of NAb-positive patients on Betaseron had titers >1,000 TRU/mL. Differences in patterns of NAb formation among the four IFNß product-dose combinations became more evident in patients with MS when both NAb frequency and the full range of NAb titer magnitude were measured.

HLA-C antigen mismatch is associated with worse outcome in unrelated donor peripheral blood stem cell transplantation.

The association between HLA matching and outcome in unrelated-donor peripheral blood stem cell (PBSC) transplantation has not yet been established. In the present study, a total of 1933 unrelated donor-recipient pairs who underwent PBSC transplantation between 1999 and 2006 for acute myelogenous leukemia, acute lymphoblastic leukemia, myelodysplastic syndrome, or chronic myelogenous leukemia and received high-resolution HLA typing for HLA-A, -B, -C, -DRB1, -DQA1, and -DQB1 were included in the analysis. Outcomes were compared between HLA-matched and HLA-mismatched pairs, adjusting for patient and transplant characteristics. Matching for HLA-A, -B, -C, and -DRB1 alleles (8/8 match) was associated with better survival at 1 year compared with 7/8 HLA-matched pairs (56% vs 47%). Using 8/8 HLA-matched patients as the baseline (n = 1243), HLA-C antigen mismatches (n = 189) were statistically significantly associated with lower leukemia-free survival (relative risk [RR], 1.36; 95% confidence interval [CI], 1.13-1.64; P = .0010), and increased risk for mortality (RR, 1.41; 95% CI, 1.16-1.70; P = .0005), treatment-related mortality (RR, 1.61; 95% CI, 1.25-2.08; P = .0002), and grade III-IV graft-versus-host disease (RR, 1.98; 95% CI, 1.50-2.62; P < .0001). HLA-B antigen or allele mismatching was associated with an increased risk for acute GVHD grade III-IV. No statistically significant differences in outcome were observed for HLA-C allele (n = 61), HLA-A antigen/allele (n = 136), HLA-DRB1 allele (n = 39), or HLA-DQ antigen/allele (n = 114) mismatches compared with 8/8 HLA-matched pairs. HLA mismatch was not associated with relapse or chronic GVHD. HLA-C antigen-mismatched unrelated PBSC donors were associated with worse outcomes compared with 8/8 HLA-matched donors. The study's limited power due to small sample size precludes conclusions about other mismatches.

Cutpoint selection for discretizing a continuous covariate for generalized estimating equations.

We consider the problem of dichotomizing a continuous covariate when performing a regression analysis based on a generalized estimation approach. The problem involves estimation of the cutpoint for the covariate and testing the hypothesis that the binary covariate constructed from the continuous covariate has a significant impact on the outcome. Due to the multiple testing used to find the optimal cutpoint, we need to make an adjustment to the usual significance test to preserve the type-I error rates. We illustrate the techniques on one data set of patients given unrelated hematopoietic stem cell transplantation. Here the question is whether the CD34 cell dose given to patient affects the outcome of the transplant and what is the smallest cell dose which is needed for good outcomes.

Marginal models for clustered time-to-event data with competing risks using pseudovalues.

Many time-to-event studies are complicated by the presence of competing risks and by nesting of individuals within a cluster, such as patients in the same center in a multicenter study. Several methods have been proposed for modeling the cumulative incidence function with independent observations. However, when subjects are clustered, one needs to account for the presence of a cluster effect either through frailty modeling of the hazard or subdistribution hazard, or by adjusting for the within-cluster correlation in a marginal model. We propose a method for modeling the marginal cumulative incidence function directly. We compute leave-one-out pseudo-observations from the cumulative incidence function at several time points. These are used in a generalized estimating equation to model the marginal cumulative incidence curve, and obtain consistent estimates of the model parameters. A sandwich variance estimator is derived to adjust for the within-cluster correlation. The method is easy to implement using standard software once the pseudovalues are obtained, and is a generalization of several existing models. Simulation studies show that the method works well to adjust the SE for the within-cluster correlation. We illustrate the method on a dataset looking at outcomes after bone marrow transplantation.