Analysis of long-term survival in multiple myeloma after first-line autologous stem cell transplantation: impact of clinical risk factors and sustained response.

The widespread use of high-dose therapy and autologous stem cell transplantation (ASCT) as well as the introduction of novel agents have significantly improved outcomes in multiple myeloma (MM) enabling long-term survival. We here analyze factors influencing survival in 865 newly diagnosed MM patients who underwent first-line ASCT at our center between 1993 and 2014. Relative survival and conditional survival were assessed to further characterize long-term survivors. Achievement of complete response (CR) post-ASCT was associated with prolonged progression-free survival (PFS) in the whole cohort and with significantly superior overall survival (OS) in the subgroup of patients receiving novel agent-based induction therapy. Landmark analyses performed at 1, 3, and 5 years post-ASCT revealed that sustainment of any response had a highly significant influence on survival with no significant differences between sustained CR and sustained inferior responses. Furthermore, outcome was independently improved by administration of maintenance therapy. A subset of patients did experience long-term survival >15 years. However, conditional survival demonstrated a persistent risk of myeloma-associated death and cumulative relative survival curves did not show development of a clear plateau, even in prognostically advantageous groups. In conclusion, in this large retrospective study, sustained response after first-line ASCT was found to be a major prognostic factor for OS independent of depth of sustained response. Administration of maintenance therapy further improved outcome, supporting the hypothesis that interventions to prolong responses achieved post-ASCT may be essential to reach long-term survival, especially in the setting of persisting residual disease.