Comparison of Characteristics and Outcomes of Trial Participants and Nonparticipants: Example of Blood and Marrow Transplant Clinical Trials Network 0201 Trial

Controversy surrounds the question of whether clinical trial participants have better outcomes than comparable patients who are not treated on a trial. We explored this question using a recent large, randomized, multicenter study comparing peripheral blood (PB) with bone marrow transplantation from unrelated donors, conducted by the Blood and Marrow Transplant Clinical Trials Network (BMT CTN). We compared characteristics and outcomes of study participants (n = 494) and nonparticipants (n = 1384) who appeared eligible and received similar treatment without enrolling on the BMT CTN trial at participating centers during the study time period. Data were obtained from the Center for International Blood and Marrow Transplant Research. Outcomes were compared between the 2 groups using Cox proportional hazards regression models. No significant differences in age, sex, disease distribution, race/ethnicity, HLA matching, comorbidities, and interval from diagnosis to hematopoietic cell transplantation were seen between the participants and nonparticipants. Nonparticipants were more likely to have lower performance status, lower risk disease, and older donors, and to receive myeloablative conditioning and antithymocyte globulin. Nonparticipants were also more likely to receive PB grafts, the intervention tested in the trial (66% versus 50%, P < .001). Overall survival, transplantation-related mortality, and incidences of acute or chronic graft-versus-host disease were comparable between the 2 groups though relapse was higher (hazard ratio, 1.22; 95% confidence interval, 1.02 to 1.46; P = .028) in nonparticipants. Despite differences in certain baseline characteristics, survival was comparable between study participants and nonparticipants. The results of the BMT CTN trial appear generalizable to the population of trial-eligible patients.