Early Reduction of Serum Free Light Chain Can Predict Therapeutic Responses in Multiple Myeloma.

Background M protein as measured by serum protein electrophoresis (SPE) is usually required for the diagnosis and therapeutic monitoring of multiple myeloma. However, SPE may not be able to detect M protein in some cases such as light-chain disease or non-secretory myeloma. Serum free light chain (FLC) assay has been recently developed and shown to be very helpful in such situations. Here, we evaluate the usefulness of this new test in the diagnosis and therapeutic monitoring of myeloma patients treated with bortezomib plus dexamethasone at our institution.

Methods Serial serum FLC assays were performed before and after each cycle of induction therapy. All patients were treated with bortezomib plus dexamethasone every 3 weeks for four cycles. Treatment responses were determined according to the European Group for Blood and Marrow Transplantation criteria.

Results There were total of 25 patients in this analysis. Fifteen were male (60%); the median age was 54 years (range, 35–68 years). Abnormal ratio of serum FLC was detected in 88% of pre-treatment serum samples. After four cycles of induction therapy, nine patients (36%) had achieved complete remission. No baseline clinical and laboratory parameters could correctly predict the therapeutic responses in these patients. When serial FLC assays were taken into account, we found that a more-than-40% reduction in the abnormal serum FLC after the first cycle of treatment was significantly associated with achieving complete response at the end of treatment (Pearson Chi-square, p = 0.041).

Conclusions Serum FLC assay is very useful for the diagnosis of multiple myeloma and allows a more rapid assessment of therapeutic response. Further studies are needed to establish the role of this test in the era of highly effective anti-myeloma therapy.