Autologous stem cell transplantation (ASCT) is a standard treatment for eligible multiple myeloma (MM) patients, but many patients will relapse after ASCT and require subsequent therapy. The proteasome inhibitor carfilzomib is approved for relapsed or refractory MM (RRMM). In phase 3 trials, carfilzomib-based regimens (ASPIRE, carfilzomib-lenalidomide-dexamethasone; ENDEAVOR, carfilzomib-dexamethasone) demonstrated superior progression-free survival (PFS) compared with standard therapies for RRMM (ASPIRE: lenalidomide-dexamethasone; ENDEAVOR, bortezomib-dexamethasone). This subgroup analysis of ASPIRE and ENDEAVOR evaluated outcomes according to prior ASCT status. In total, 446 patients in ASPIRE and 538 in ENDEAVOR had prior ASCT. Median PFS was longer for carfilzomib-based regimens vs non-carfilzomib-based regimens for patients with prior ASCT (ASPIRE: 26.3 vs 17.8 months (hazard ratio (HR) = 0.68); ENDEAVOR: not estimable vs 10.2 months (HR = 0.61)), those with one prior line of therapy that included ASCT (ASPIRE: 29.7 vs 17.8 months (HR = 0.70); ENDEAVOR: not estimable vs 11.2 months (HR = 0.46)), and those without prior ASCT (ASPIRE: 26.4 vs 16.6 months (HR = 0.76); ENDEAVOR: 17.7 vs 8.5 months (HR = 0.43)). Overall response rates also favored the carfilzomib-based regimens. No new safety signals were detected. This analysis suggests that carfilzomibbased treatment may lead to improvement in PFS and response rates regardless of prior transplant status. Further evaluation is warranted.