Prognostic Implications of Rising Serum Monoclonal Protein and Free Light Chains after Autologous Stem Cell Transplantation in Patients with Multiple Myeloma

Patients who undergo autologous stem cell transplantation (ASCT) for multiple myeloma (MM) are routinely assessed at day +100 using serum and urine protein electrophoresis/immunofixation and the serum free light chain (sFLC) assay. We evaluated whether an increase in M-spike or FLC from immediately before ASCT to day +100 post-ASCT has any prognostic impact. We retrospectively reviewed 1218 patients with MM at the Mayo Clinic who underwent their first ASCT between 2000 and 2016. We stratified patients into those with a rise in M-spike by at least 0.1 g/dL from immediately before ASCT to day +100 post-ASCT (M-spike cohort 1) and those who did not (M-spike cohort 2). We also stratified patients into those with a rise in the involved FLC by at least 5 mg/dL (FLC cohort 1) and those who did not (FLC cohort 2). Survival analysis for progression-free survival (PFS) and overall survival (OS) was performed using the Kaplan-Meier method. A rise in M-spike by at least 0.1 g/dL from pre-ASCT to day +100 was seen in 53 patients (4.3%). The median PFS and OS were found to be significantly shorter in M-spike cohort 1 compared with their counterparts (median PFS, 10 months versus 26 months [P < .0001]; median OS, 35 months versus 79 months [P < .0001]). An increase in involved FLC by at least 5 mg/dL was observed in 25 patients (2.3%). Similarly, the median PFS and OS were found to be inferior in FLC cohort 1 compared with FLC cohort 2 (median PFS, 4 months versus 28 months [P < .0001]; median OS, 11 months versus 82 months [P < .0001]). An increase of M-spike by at least 0.1 g/dL and an increase in involved FLC by at least 5 mg/dL from pre-ASCT to day +100 increases the likelihood of an early relapse after ASCT, and these patients may benefit from closer surveillance after day +100.