Day 21 serum Free Light Chain (FLC) levels as a predictor of response to therapy in symptomatic multiple myeloma

Abstract

Objective: To study the predictive value of reduction of involved free light chain level on Day 21 of chemotherapy for achievement of VGPR after 4 cycles of induction chemotherapy.
Methods: We conducted a prospective observational study in twenty eight patients of newly diagnosed Multiple Myeloma with iFLC  ≥ 100mg/L. Serum FLC assay was done at baseline and on day 21 of therapy. All patients were followed up till the end of induction therapy for response assessment based on the IMWG criteria. Receiver Operator Characteristic (ROC) curve analysis was done to determine the cut off value of percent reduction in day 21 iFLC for achievement of VGPR or better.
Results: After the induction chemotherapy, out of 28 patients, 13 patients achieved CR, 8 patients achieved VGPR, 4 patients achieved PR and 2 patients had stable disease (≥ VGPR = 21 patients, < VGPR = 6 patients). One patient expired after 2^nd cycle of chemotherapy. The mean per cent reduction in day 21 iFLC level as compared to baseline was 91.5% and 57.1% in patients achieving ≥ VGPR and < VGPR (P < 0.0001), respectively. No other baseline parameter was found to be significantly different between the 2 groups.  ROC curve analysis demonstrated a cut off of 84% reduction in iFLC value on day 21 (AUC of 0.937) had a sensitivity of 85.7% and a specificity of 100% in predicting the achievement of VGPR after four cycles of induction chemotherapy.
Conclusion: Monitoring iFLC levels on Day 21 can be used as an important tool for early identification of responders/non responders to myeloma therapy. We recommend serum FLC assay to be done on day 21 as a real time assessment of treatment response in newly diagnosed myeloma patients. Key words- Multiple Myeloma, involved Free Light Chain (iFLC), Very Good Partial Response (VGPR)