CLINICAL TRIALS AND OBSERVATIONS High serum-free light chain levels and their rapid reduction in response to therapy define an aggressive multiple myeloma subtype with poor prognosis

Serum-free light chain (SFLC) levels are useful for diagnosing nonsecretory myeloma and monitoring response in lightchain–only disease, especially in the presence of renal failure. As part of a tandem autotransplantation trial for newly diagnosed multiple myeloma, SFLC levels were measured at baseline, within 7 days of starting the first cycle, and before both the second induction cycle and the first transplantation. SFLC baseline levels higher than 75 mg/dL (top tertile) identified 33% of 301 patients with higher near-complete response rate (n-CR) to induction therapy (37% vs 20%, P .002) yet inferior 24month overall survival (OS: 76% vs 91%, P < .001) and event-free survival (EFS: 73% vs 90%, P < .001), retaining independent prognostic significance for both EFS (HR 2.40, P .008) and OS (HR 2.43, P .016). Baseline SFLC higher than 75 mg/dL was associated with light-chain–only secretion (P < .001), creatinine level 176.8 M (2 mg/dL) or higher (P < .001), beta-2-microglobulin 297.5 nM/L (3.5 mg/L) or higher (P < .001), lactate dehydrogenase 190 U/L or higher (P < .001), and bone marrow plasmacytosis higher than 30% (P .003). Additional independent adverse implications were conferred by toptertile SFLC reductions before cycle 2 (OS: HR 2.97, P .003; EFS: HR 2.56, P .003) and before transplantation (OS: HR 3.31, P .001; EFS: HR 2.65, P .003). Unlike baseline and follow-up analyses of serum and urine M-proteins, high SFLC levels at baseline—reflecting more aggressive disease—and steeper reductions after therapy identified patients with inferior survival. (Blood. 2007; 110:827-832)