Role of Free Light Chain Assay Ratio to Distinguish Between CR According EBMT Criteria or Stringent Complete Remission (sCR) According IMWG in Multiple Myeloma Patients.

The qualitative assay for free light chain has been reported to be sensitive and specific for detecting and monitoring diseases caused by monoclonal gammopathies such as multiple myeloma. More recently the International Myeloma Working Group proposed uniform response criteria including a new definition of stringent complete remission (sCR). The definition of stringent complete remission requires beside absence of clonal cells in bone marrow by immunohistochemistry or immunofluorescence also normalization of free light chain ratio in serum.

We evaluate the value of free light chain assay to determine stringent CR by monitoring 87 patients with multiple myeloma who achieved complete remission (n=52) or very good partial remission (n=35) between January 2003 and December 2008. Free light chain measurements were performed with the commercially available Free lite^TM Kit (Binding Site, Heidelberg, Germany). Because of the shorter half-life of free light chain assay ratio, only patients were included, if the complete or very good partial remission remains stable for at least 3 months. The comparison between immunofixation and free light chain ratio was performed at least 6 weeks after immunofixation becomes negative for the first time. 87 patients (50 mal and 37 female) were included, 67 had intact immunoglobulin and 11 had light chain immunoglobulin at time of diagnosis. The remission status was determined either after allogeneic (n = 73) or autologous (n = 7) stem cell transplantation or after conventional bortezomib or lenalidomide containing chemotherapy (n = 7).

35 out of 87 patients achieved a very good partial or near complete remission with still positive immunofixation. In 22 out of those 35 patients the free light chain kappa ratio was within the normal range of 0.26 – 1.65 mg/l (63 %). Only in 13 patients with persistent immunofixation positivity the free light chain ratio was outside the normal range (37%). 52 patients achieved complete remission according to the EBMT criteria with negative immunofixation for at least 3 months. In those patients all (100 %) had a normal free light chain kappa/lambda ratio. In a subgroup of patients (n = 10) who relapsed during follow-up from complete remission sequential monitoring of immunofixation and free light assay was performed as recently described [4]. In 9 out of 10 patients a free light chain ratio became abnormal at a median 90 days before immunofixation became positive.

The free light chain assay ratio is a useful marker for a faster detection of remission or progression in myeloma patients. However, these results do not support additional value of free light chain ratio to determine the depth of remission in immunofixation negative patients. More sensitive methods such as imunophenotyping analysis by FACS or molecular primer should be used to determine depth of complete remission since these methods have shown relevant clinical impact.

No relevant conflicts of interest to declare.