Evaluation of Serum Free Light Chains and Outcome in Multiple Myeloma Patients with an Intact Monoclonal Immunoglobulin Treated with Autologous Stem Cell Transplantation.

Introduction: The serum free light chain (FLC) assay is a useful tool in diagnosing and monitoring multiple myeloma (MM) patients (pts) with non-secretory and light chain only disease. In addition, the detection of an abnormal serum FLC ratio is an adverse prognostic factor in pts with monoclonal gammopathy of undetermined significance. However, the relationship of the FLC assay to the outcome of patients with an intact monoclonal immunoglobulin following a single autologous stem cell transplantation (ASCT) has not been studied. Thus, the objective of this single centre, retrospective review study was to evaluate the usefulness of the FLC assay as a predictor for response rate and progression free survival (PFS) in this category of pts. Patients & Methods: We identified in our Princess Margaret Hospital MM database a total of 290 pts who underwent a single ASCT between June 2003 and May 2006. Of these, 65 had an intact monoclonal immunoglobulin (IgG in 47, IgA in 16 and IgD in 2) detected at diagnosis plus FLCs measured at referral. Normal range for FLC measurements is as follows: kappa 3.3–13.1 mg/L, lambda 5.7–26.3 mg/L, and kappa/lambda ratio of 0.26–1.65. Results: The median age at diagnosis was 59 years (range, 34–73); 33 (51%) were male. The median time from diagnosis to ASCT was 9.0 months (range, 5.0–29), with a median follow-up time of 27 months (range, 1.0–58.0). Assessment of best response following ASCT revealed that 20 (31%) pts achieved CR/nCR, 21 (32%) VGPR, 21 (32%) PR, 2 (3%) MR, and 1 (2%) was not evaluable for response. No prognostic factors for response were identified. To date, only 9 pts have died and the median overall survival is not yet reached. The median PFS is 25.4 months, with 36 patients progressing after ASCT. An elevated kappa and lambda light chain was detected in 30 (46%) and 22 (34%) of the 65 pts, respectively. Additionally, 52 (82%) of the 65 pts were found to have an abnormal kappa/lambda ratio. There was no significant difference in the PFS of patients with abnormal vs. normal free kappa light chains or FLC ratio. However, a decreased PFS was associated with elevated levels of serum free lambda light chains (p=0.01), β-2 microglobulin (p=0.007) and LDH (p=0.01). Conclusions: The majority of pts with an intact monoclonal immunoglobulin also have an abnormally high level of the corresponding serum FLC and an abnormal FLC ratio; an elevated serum free lambda level as well as increased β-2 microglobulin and LDH levels, as previously described, were identified as adverse prognostic factors for PFS in this population; we continue to routinely assess serum FLC for all pts at referral; however, longer follow-up is needed to further evaluate the prognostic significance of this parameter on the clinical outcome of pts.