Limited guidance exists for dosing
melphalan for autologous
stem cell transplantation (ASCT) in the obese patient population, because the current literature reports conflicting clinical outcomes between obese and nonobese patients. In 2014, the American Society for Blood and Marrow
Transplantation published conditioning
chemotherapy dosing guidelines for obese patients and recommended dosing of
melphalan using actual
body weight (ABW) in the body surface area calculation. The practice at Barnes-Jewish Hospital has consistently been to dose
melphalan using adjusted
body weight (AdBW), with a 20% correction when a patient weighs ≥120% of his or her ideal body weight (IBW). The purpose of this study was to compare outcomes of
melphalan ASCT in patients with
multiple myeloma between obese (≥120% IBW) and nonobese (<120% IBW) populations. This retrospective, single-center study included adult patients with
multiple myeloma undergoing first ASCT with
melphalan conditioning between January 2009 and December 2012. Patient demographic data,
transplantation characteristics, and clinical outcomes were collected. The primary outcome was 3-year event-free survival (EFS). Secondary outcomes included response at 100 days post-
transplantation, 3-year overall survival, treatment-related mortality (TRM), time to neutrophil engraftment, and hospital
length of stay (LOS). To ensure that
melphalan dosage adjustment in the obese population did not impact efficacy, the primary outcome was assessed using a noninferiority design, with a predetermined noninferiority margin of 7%. Assuming a 70% 3-year EFS in the nonobese population, a noninferiority margin of 7%, a power of 80%, and an α value of .05, an analysis of 280 patients was required. A total of 270 patients, including 171 (63%) obese patients and 99 (37%) nonobese patients, met our inclusion criteria. Baseline characteristics were well matched between the 2 cohorts, including high-risk cytogenetics, disease severity at diagnosis, and use of maintenance
therapy, with the only detectable differences related to weight itself. The 3-year EFS was 41% for the total cohort, with fewer events occurring in the obese cohort compared with the nonobese cohort (51% versus 40%; P = .0025). The 95% lower confidence limit established noninferiority. High-risk cytogenetics, disease severity at diagnosis, and
therapy response pre- and post-ASCT were all associated with significantly shorter EFS. No between-group differences in TRM, time to engraftment, or hospital LOS were noted. This retrospective, single-center study found that using AdBW to dose
melphalan in obese patients was not inferior to the nonobese population in terms of 3-year EFS. This study adds to the limited evidence on
melphalan dosing and suggests that
transplantation efficacy is not affected by AdBW dosing in obese patients. Further studies are needed to provide additional insight into the pharmacokinetic differences and best dosing practices for obese patients.