Response Assessment Criteria for Light Chain Multiple Myeloma

Measurable Disease Criteria

Light chain multiple myeloma is considered measurable when the involved serum free light chain (FLC) level is ≥10 mg/dL and the FLC ratio is abnormal, as per the International Myeloma Working Group (IMWG) criteria 2, 1
All measurable parameters should be followed, with particular emphasis on serum FLC measurements for light chain myeloma, as recommended by the Journal of Clinical Oncology 3, 1

The National Comprehensive Cancer Network (NCCN) defines complete response criteria plus normal FLC ratio (0.26-1.65) and absence of clonal plasma cells in bone marrow by immunohistochemistry or flow cytometry 4, 1

The NCCN recommends negative immunofixation on serum and urine, disappearance of any soft tissue plasmacytomas, and <5% plasma cells in bone marrow aspirate 6
For patients whose only measurable disease is by serum FLC, the NCCN requires negative serum and urine immunofixation plus normal FLC ratio on two consecutive assessments 2, 5

The NCCN defines VGPR as serum and urine M-protein detectable by immunofixation but not on electrophoresis, or ≥90% reduction in serum M-protein plus urine M-protein <100 mg/24h 6
For patients whose only measurable disease is by serum FLC, the NCCN requires >90% decrease in the difference between involved and uninvolved FLC levels on two consecutive assessments 2, 5

The NCCN recommends ≥50% reduction in serum M-protein and reduction in 24-hour urinary M-protein by ≥90% or to <200 mg/24h 4, 6
For patients whose only measurable disease is by serum FLC, the NCCN requires ≥50% decrease in the difference between involved and uninvolved FLC levels 4, 1

For patients whose only measurable disease is by serum FLC, the NCCN defines PD as ≥25% increase from lowest response value in the difference between involved and uninvolved FLC levels (absolute increase must be >10 mg/dL) 4, 6

The Journal of Clinical Oncology recommends response assessments be performed after one cycle of therapy, then every other cycle once a response trend is observed, and less frequently once the patient reaches plateau phase 3
All responses (except for bone marrow and imaging assessments) should be confirmed with a second measurement, as recommended by the Journal of Clinical Oncology and Blood 3, 2
The European Journal of Nuclear Medicine and Molecular Imaging suggests PET/CT imaging can complement serum and urine assessments, particularly for evaluating extramedullary disease 7, 8