Serum Free Light Chain [FLC] Assay in Multiple Myeloma Patients Who Achieved Negative Immunofixation after Allogeneic Stem Cell Transplantation.

The quantitative assay for free light chains [FLC] has been reported to be sensitive and specific for detecting and monitoring free light chain diseases such as multiple myeloma. To evaluate the sensitivity of FLC for monitoring patients in complete remission for early detection of relapse, the measurement of more than 250 serum free light chains were performed with the commercial available Freelite ^TM kit [Binding Site] in 26 patients who achieved complete remission with negative immunofixation after dose reduced allogeneic stem cell transplantation. The patient groups were divided in those who remained immunofixation negative [n=12, group 1] during follow-up of at least 1 year and those who had been immunofixation negative but became positive during follow-up [n=9, group 2] and those who had achieved near complete remission with positive immunofixation but then became immunofixation negative during follow-up [n=5, group 3]. In group 1 the measuring of 105 FLC concentration and kappa/lambda ratio was performed in 12 patients. In 10 patients [83 %] free light concentration of kappa or lambda remained within the normal range during follow-up of more than 1 year. In 2 patients [17 %] kappa or lambda FLC concentration was above the normal range, but remained stable without any signs of increasing amount. Group 2 consisted of 9 patients who had been immunofixation negative but became positive during follow-up. In all patients an increase of the corresponding free light chain could be observed in serum. In 4 patients a very close monitoring of immunofixation and free light assay was performed and an at least 25 % increase of the free light concentration in serum was observed at a median of 97 days before immunfixation became positive. In group 3 five patients who had been immunofixation positive became negative during follow-up. In all of the patients the free light concentration was within the range at time of negative immunofixation. The corresponding free light concentration dropped down and reached normal level at a median of 38 days before the patients had achieved negativity of immunofixation. These results suggest that serum free light chain assay allows monitoring of patients with complete remission and might detect early relapse before immunofixation becomes positive. Thus, an early increase of free light chain assay in immunofixation negative patients after allogeneic transplantation might be an useful guide for adoptive immunotherapy strategies to prevent clinical relapse.