Impact of Second Primary Malignancy Post-Autologous Transplantation on Outcomes of Multiple Myeloma: A CIBMTR Analysis

The overall survival (OS) has improved significantly in multiple myeloma (MM) over the last decade with use of proteasome inhibitor and immunomodulatory drug-based combinations, followed by high-dose melphalan and autologous hematopoietic stem cell transplantation (auto-HSCT) and subsequent maintenance therapies in eligible newly diagnosed patients. However, clinical trials employing auto-HSCT followed by lenalidomide maintenance have shown an increased risk of second primary malignancies (SPM), including second hematological malignancies (SHM). We evaluated the impact of SPM and SHM on progression-free survival (PFS) and OS in MM patients following auto-HSCT using CIBMTR registry data. Adult MM patients who underwent first auto-HSCT in the United States with melphalan conditioning regimen from 2011 to 2018 and received maintenance therapy were included (n=3,948). At a median follow up of 37 months, 175 (4%) patients developed SPM, including 112 (64%) solid, 36 (20%) myeloid, 24 (14%) SHM, not otherwise specified, and 3 (2%) lymphoid malignancies. Multivariate analysis demonstrated that SPM and SHM were associated with an inferior PFS (HR 2.62, P<.001 and HR 5.01, P<.001, respectively) and OS (HR 3.85, P<.001 and HR 8.13, P<.001, respectively). In patients who developed SPM and SHM, MM remained the most frequent primary cause of death (42% versus 30% and 53% versus 18%, respectively). We conclude the development of SPM and SHM leads to a poor survival in MM patients and is an important survivorship challenge. Given the median survival for MM continues to improve, continued vigilance is needed to assess the risks of SPM and SHM with maintenance therapy post-auto-HSCT.