Diagnostic and Response Criteria for Light Chain Multiple Myeloma

Diagnostic Criteria

The National Comprehensive Cancer Network recommends complete blood count with differential and platelet counts for diagnostic testing 1
Blood chemistry including BUN, creatinine, electrolytes, calcium, albumin, LDH, and beta-2 microglobulin is recommended for diagnostic testing 1, 2
Serum free light chain (FLC) assay with kappa/lambda ratio is used for diagnostic testing 1, 2, 3
24-hour urine collection for total protein, urine protein electrophoresis (UPEP), and urine immunofixation electrophoresis (UIFE) is recommended for diagnostic testing 1, 4
Bone marrow aspiration and biopsy with immunohistochemistry and/or flow cytometry is used for diagnostic testing 1, 2
Cytogenetic studies including FISH analysis are recommended for diagnostic testing 1, 2
Skeletal survey (X-ray, CT, or MRI) is used for diagnostic testing 4, 5
The International Myeloma Working Group defines light chain multiple myeloma as having ≥10% clonal bone marrow plasma cells or biopsy-proven plasmacytoma 5, 6
Abnormal serum free light chain ratio with elevated involved light chain is a diagnostic criterion 1, 3
Evidence of end-organ damage (CRAB criteria) is a diagnostic criterion 5, 6

The National Comprehensive Cancer Network recommends using serum free light chain measurements for monitoring response 1, 3
Stringent Complete Response (sCR) is defined as complete response criteria plus normal FLC ratio and absence of clonal plasma cells in bone marrow by immunohistochemistry or flow cytometry 1, 3, 6
Complete Response (CR) is defined as negative immunofixation of serum and urine, disappearance of any soft tissue plasmacytomas, and <5% plasma cells in bone marrow 1, 5
Very Good Partial Response (VGPR) is defined 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 1, 5
Partial Response (PR) is defined as ≥50% reduction of serum M-protein and ≥90% reduction in 24h urinary light chain excretion or to <200 mg/24h 1

Serum FLC assay cannot completely replace 24-hour UPEP for monitoring patients with measurable urinary M-protein 1, 3
FLC measurements can be affected by renal function, potentially leading to false elevations 1
After quantifying the involved light chain, it's crucial to use the same test for serial measurements to ensure accurate relative quantification 1, 3