Prediction of response and progression in multiple myeloma with serum free light chains assay: corroboration of the serum free light chain response definitions.
BACKGROUND
The International Myeloma Working Group (IMWG) proposed response and progression criteria using serum free light chain (sFLC) testing for patients with nonsecretory multiple myeloma (MM). We attempt to validate these criteria by comparing paraprotein responses with sFLC responses in patients with secretory myeloma.


METHODS
Prospectively entered data for 89 patients with MM enrolled on various clinical trials at the Cleveland Clinic between April 2004 and December 2006 were reviewed.


RESULTS
By standard paraprotein criteria, 4 patients had complete remission (CR), 22 had partial remission (PR), 34 had stable disease (SD), 26 had progressive disease (PD), and 3 were inevaluable. Only 43 patients (48%) had an involved sFLC > or = 10 mg/dL (which is considered evaluable by the IMWG), of which 14 had PR, 8 had SD, 18 had PD, and 3 were inevaluable. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for sFLC in predicting response were 81%, 83%, 64%, and 92% respectively. The sensitivity, specificity, PPV, and NPV for sFLC in predicting progression were 93%, 80%, 72%, and 95% respectively.


CONCLUSIONS
sFLC reliably predicts response and progression in MM. However, half of the patients had inevaluable disease by sFLC, thus limiting the utility of sFLC testing in patients with nonmeasurable disease by electrophoretic methods.
Khoriaty
Rami
R
University of Michigan Hematology and Oncology Fellowship Program, Ann Arbor, MI, USA.
Hussein
Mohamad A
MA
Faiman
Beth
B
Kelly
Megan
M
Kalaycio
Matt
M
Baz
Rachid
R
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016026:Bone Marrow Transplantation; D003404:Creatinine / Q000097:blood; D018450:Disease Progression; D005260:Female; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000097:blood* / Q000401:mortality; D011379:Prognosis; D011446:Prospective Studies
D007147:Immunoglobulin Light Chains; D003404:Creatinine