Long-Term Outcomes in Patients with Plasma Cell Myeloma Following High-Dose Chemotherapy with Autologous Stem Cell Transplantation

Plasma cell myeloma (PCM) is a hematopoietic malignancy characterized by the neoplastic proliferation of clonal plasma cells in the bone marrow. High-dose chemotherapy (HDCTx) followed by autologous stem cell transplantation (ASCT) is considered the standard of care treatment for eligible patients. Although the introduction of new therapeutic agents has further contributed to improved survival outcomes, the disease remains incurable, with most patients eventually experiencing relapse or disease progression. Circulating tumor cells at the time of stem cell collection that are reinfused with the autograft may be one of the factors influencing the clinical outcomes. The objective of this study was to evaluate the association of patient- and treatment-related parameters with progression-free survival (PFS) and overall survival (OS) in PCM patients who underwent ASCT. The survival data of 204 patients diagnosed with PCM who received ASCT between 2010 and 2014 at the University Hospital Zurich were collected and analyzed. Most patients received proteasome inhibitor- or immunomodulatory drug-based induction therapy followed by high-dose melphalan conditioning before ASCT. The median PFS was 33.3 months and the median OS was 65.1 months. In patients with follow-up data of at least 5 years (n=174), the estimated 5-year OS rate was 68.4%. The median number of reinfused CD34^+^ cells was 3.77x10^6^ per kg body weight per reinfusion. In patients who received single ASCT (n=144), no significant difference was observed based on the mean number of reinfused CD34^+^ cells (three tiers: <2.65x10^6^ vs 2.66−4.49x10^6^ vs >4.49x10^6^ CD34+ cells per kg body weight per reinfusion) in terms of OS (p=0.103) and PFS (p=0.704). There was also no significant difference in OS (p=0.786) and PFS (p=0.425) correlated with remission status on the day of ASCT. In conclusion, this study suggests that the anticipated influences of graft composition no longer play a major role in the era of modern second- and subsequent lines of therapies. HDC and ASCT remain the mainstay of therapy for eligible patients and further investigations into variables influencing the outcome of PCM patients are warranted.