Blood, 15 May 2008, Vol. 111, No. 10, pp. 4908-4915.
Prepublished online as a Blood First Edition Paper on March 25, 2008; DOI 10.1182/blood-2008-02-138602.
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CLINICAL TRIALS AND OBSERVATIONS
Appraisal of immunoglobulin free light chain as a marker of response
Angela Dispenzieri1,2,
Lijun Zhang3,
Jerry A. Katzmann2,
Melissa Snyder2,
Emily Blood4,
Roberta DeGoey1,
Kimberly Henderson1,
Robert A. Kyle1,2,
Martin M. Oken5,
Arthur R. Bradwell6, and
Philip R. Greipp1,3
Departments of1 Hematology and
2 Laboratory Medicine, Mayo Clinic, Rochester, MN;
3 Department of Biostatistics, Eastern Cooperative Oncology Group (ECOG), Boston, MA;
4 Dartmouth Medical School, Lebanon, NH;
5 University of Minnesota, Minneapolis; and
6 Department of Immunology, Birmingham University Medical School, Birmingham, United Kingdom
The immunoglobulin free light chain (FLC) assay is an invaluable tool for following patients with oligosecretory plasma cell dyscrasia. Baseline values have also been shown to be prognostic in all plasma cell disorders tested. A looming question, however, is the role it should play in following myeloma patients with disease that is measurable using serum and urine electrophoresis. We used the data and stored samples from a mature Eastern Cooperative Oncology Group clinical trial (E9486) to assess serum levels of FLC at baseline and after 2 months of alkylator-based therapy. For serial determinations, the absolute level of involved serum FLC or the difference of the involved and uninvolved FLC is preferred over the ratio of involved to uninvolved FLC. FLC response after 2 months of therapy was superior to early M-protein measurement to predict overall response. The ideal cut-point for FLC change appears to be between 40% and 50% reduction. The correlation between serial measurements of serum FLC and urine M-protein is inadequate to abolish the serial 24-hour urine protein. Although baseline values of FLC are prognostic in newly diagnosed myeloma patients, serial measurements do not appear to have added value in patients who have M-proteins measurable by electrophoresis.
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