Tandem Autologous Stem Cell Transplantation Does Not Benefit High-Risk Myeloma Patients in the Maintenance Era: Real-World Results from The Canadian Myeloma Research Group Database

In patients with multiple myeloma (MM), the presence of high-risk cytogenetic abnormalities is associated with worse disease control and survival. Autologous stem cell transplant (ASCT) does benefit these patients. Tandem transplantation has been explored as a means to deepen responses and further improve survival however, its role remains controversial. This is particularly true in the era of novel agent induction and post-transplant maintenance therapy. The aim of this study was to use the Canadian Myeloma Research Group database and examine a large cohort of real-world patients comparing the outcomes of tandem versus single ASCT specifically in high-risk patients receiving novel agent-based induction and post-transplant maintenance. The data for this study was derived retrospectively from a comprehensive national-level database of Canadian patients with MM. High-risk cytogenetics was defined as presence of del17p, t(4;14), or t(14;16). Those receiving allogeneic transplant were excluded. Tandem transplantation was defined as a second ASCT performed consecutively without interim relapse or progression after first ASCT. Those with relapse or progressive disease within 3 months of completing a first transplant were excluded. We compared response depth, progression-free, and overall survival (OS) based on single or tandem transplantation procedures. The impact of covariates of interest was also assessed. A total of 381 patients with high-risk cytogenetics were identified. A total of 242 received single and 139 patients received tandem transplants. All received post-transplant maintenance. The most common induction regimen for these patients was cyclophosphamide, bortezomib, and steroids (CyBorD, 87%). Forty-one patients (10.8%) required reinduction prior to first ASCT. The best overall responses at any time were 98.3% (90.5% ≥ very good partial response [VGPR]) and 98.6% (89.9% ≥ VGPR) in the single and tandem ASCT groups, respectively. Survival outcomes were similar with the median progression-free survival for single or tandem ASCT of 35.2 and 35.3 months (P = .88) and the median OS were 92.6 and 88.9 months, respectively (P = .72). No statistically significant differences were seen based on type of cytogenetic abnormality or type of maintenance. This was confirmed on multivariate analysis. In the real-world setting, tandem ASCT does not improve outcomes for MM patients with high-risk cytogenetics. This may be driven by the use of effective pre- and post-ASCT therapies. The development of more potent induction and consolidation along with current nearly ubiquitous continuous maintenance therapies until disease progression does not support the use of a second high-dose procedure.