We conducted a retrospective study comparing posttransplant outcomes between myeloma patients receiving conditioning melphalan on day-2 vs day-1 for autologous stem cell transplant. Between January 2017 and December 2018, 201 patients received melphalan on day-2 and 166 on day-1 prior to stem cell infusion. Baseline disease and clinical characteristics between the two groups were similar. Although rates of hospitalization were similar between the cohorts, duration of hospital admission was longer for day-1 (median 7 days for day-1 vs 5 days for day-2, p = 0.003). Rates of fever were higher in the day-1 cohort (69% vs 49%, p = 0.0002). Time to platelet and neutrophil engraftment was significantly longer in the day-1 cohort (platelet engraftment median days 17 for day-1 vs 15 for day-2, p < 0.0001, neutrophil engraftment median days 16 for day-1 vs 16 for day-2, p = 0.025). Overall response rate was similar between the cohorts (99% for day-1, vs 100% for day-2). Day-2 melphalan infusions should be considered in preference for day-1 protocols, given the clinically significant delay in platelet and neutrophil engraftment and longer duration of hospitalization with day-1 infusions.
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