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Published: November 2009Print Record of Viewing
Dr. Katzmann discusses the 2009 Guidelines for Disease Monitoring from the International Myeloma Working Group.
Presenter: Dr. Jerry Katzmann
This presentation is provided by Dr. Jerry Katzmann, from the Division of Clinical Biochemistry and Immunology at Mayo Clinic. Dr. Katzmann will be discussing the 2009 Guidelines for Disease Monitoring from the International Myeloma Working Group.
With the introduction of the quantitative free light chain assay, the guidelines for monitoring monoclonal gammopathies have recently changed. This presentation will review the current laboratory practice for monitoring monoclonal gammopathies.
This first slide illustrates some important concepts of plasma cell proliferative diseases. The 3 sections of this slide show a Wright-Giemsa-stained bone marrow with a large number of plasma cells, below that is an immunofluorescent stain for cytoplasmic Kappa light chains showing monoclonality of the plasma cells, and on the right of this slide is a bone scan showing bone lesions resulting from foci of proliferating plasma cells.
The concepts that I want to illustrate are first, the disease resides in the bone marrow and is not uniformly distributed throughout the body. That means that monitoring disease by directly quantitating plasma cells in bone marrow biopsies is problematic. Second, the immunofluorescent micrograph illustrates what plasma cells do best – they synthesize immunoglobulins. The secreted, monoclonal immunoglobulin serves as a tumor marker, which we can measure in the serum and/or urine, and which we use to monitor disease.
The International Myeloma Working Group has recommended using serum and urine M-spikes, if they are sufficiently large to allow assessment of response. This slide shows the definition of a measurable M-spike, that is >1 g/dL in serum, and >200 mg/24 hour in urine.
On this next slide is an example of a measurable serum M-spike. The upper portion of the figure is a serum protein electrophoresis and immunofixation electrophoresis of serum from a normal donor. The lower portion is from a patient with multiple myeloma. You can see that this patient has a monoclonal IgG kappa protein from the IFE or immunofixation electrophoresis gel and that the PEL or protein electrophoresis scan quantitates the M-spike as 3.8 g/dL.
On this next slide, we have the electrophoretic results for the serum and urine from a patient with light chain multiple myeloma. The serum contains a monoclonal lambda light chain, seen in the IFE lambda lane, but it is not measurable. The urine, however, has a 2.6 g/24 hour M-spike. These 2 patients each have a measurable M-spike for monitoring response.
The International Myeloma Working Group has defined responses. A 25% to 49% reduction is a minimal response, and a 50% reduction in the serum M-spike is a partial response. The IgG kappa patient we saw on a previous slide would need the M-spike to go from 3.8 g/dL to <1.9 g/dL to be considered a partial responder. For a complete response, we would, of course, need the complete absence of a detectable serum monoclonal protein. These same guidelines require a 90% reduction in the urine M-spike for a partial response. And, the patient with the lambda light chain myeloma would need the urine M-spike to go from 2.6 g/24 hour to <0.3 g/24 hour to be considered a partial response.
In addition to the common use of serum and urine M-spikes, there are nephelometric assays that can also be used for disease monitoring. This slide lists nephelometric quantitation of serum immunoglobulin and serum free light chains. Quantitation of serum Ig by nephelometry, however, cannot be used in all monoclonal gammopathies.
This next patient, for example, has a mixture of polyclonal and monoclonal IgG. The protein electrophoresis M-spike focuses on the narrow monoclonal protein region, whereas the IgG quantitation would, in essence, measure the entire gamma fraction.
Now compare this to patients with large M-spikes. They often have suppression of the polyclonal immunoglobulins. In this patient, the nephelometric IgG serves as a good measurement for the clonal plasma cells. Many clinicians order both the serum PEL as well as serum IgG quantitation, and both methods should be changing in the same direction. They are not, however, equivalent and this sometimes leads to confusion.
We have compared electrophoretic and nephelometric quantitation of monoclonal proteins. And in this slide, you can see that the relationships are dependent on the heavy chain isotype. IgA monoclonal proteins yield a good relationship with a slope of 1. That is, the IgA M-spike correlates well with IgA by nephelometry. IgM also yields a linear relationship, but nephelometric results are 80% higher than IgM M-spikes. And lastly, IgG monoclonal proteins do not have a linear relationship. We believe that the nonlinearity is due to gel saturation when IgG M-spikes are >3 g/dL.
This has led us to conclude that although serum protein electrophoresis M-spikes are better for monitoring most monoclonal proteins, nephelometric quantitation is probably better for large M-spikes. In addition, as has been known for a long time, because quantitation is different by the 2 methods, clinicians should not go back and forth when monitoring patients.
Because physicians order both electrophoretic and nephelometric assays, we have tried to assess the variability of each assay during disease monitoring. In this study, we identified patients who had monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM), and multiple myeloma, and who also had stable disease as well as a minimum of 4 assays over a period of 1 to 5 years. Both nephelometric and electrophoretic assays have comparable analytic CVs of 4% to 5%, and when we also include long-term biologic variability, the total CVs over time are between 8% to 10%. These numbers suggest that the International Myeloma Working Group recommendations of at least a 25% change in serum M-spike for a minimum response may be too conservative.
With the use of the serum M-spike and Ig quantitation and urine M-spike, there still are some patients with no measurable disease. This slide shows the serum and urine electrophoresis results for a patient with primary amyloid. There is a faint monoclonal lambda band visible in the urine immunofixation gel, but there is no M-spike to monitor this disease even though this patient has proteinuria and a life-threatening disorder.
The introduction of the nephelometric assay to quantitate free light chains has provided a solution to this problem. The assay has specificity for free light chains and will not bind light chains that are complexed to heavy chains. That means that even in the presence of large amounts of polyclonal immunoglobulin, the assay can measure small amounts of the light chains. The complete assay is really 2 separate measurements to quantitate kappa free light chain and lambda free light chain concentrations and also to calculate the kappa:lambda free light chain ratio.
This composite slide has a few different groups of patients. The light gray area represents the kappa and lambda reference range determined from normals, plotted as blue circles. Older normals with reduced renal clearance, shown as red dots, as well as polyclonal hypergammaglobulinemia patients, shown as green squares, may fall outside these ranges.
When the data is viewed as the kappa:lambda ratio, however, all those samples fall within the reference range, but the kappa and lambda light chain myelomas are abnormal. The point I want to make with this slide is the yellow circles. These are nonsecretory myelomas that have no measurable M-spikes. Yet you can clearly see that many of these patients now have a “tumor marker” that can be used to monitor their disease.
The spectrum of measurements for disease monitoring therefore includes serum protein electrophoresis, urine protein electrophoresis, and nephelometry for serum Ig and free light chain.
The most recent guidelines for disease monitoring suggest using electrophoresis if there is a measurable M-spike. But, if there is no measurable M-spike and the serum free light chain is abnormal plus the involved free light chain is >10 mg/dL, then use the serum free light chain for monitoring.
The response criteria for a measurable, monoclonal serum free light chain is similar to the criteria for the serum M-spike. A 50% reduction in the free light chain concentration is considered a partial response, and a complete response is normalization of the free light chain ratio, plus normal immunofixation and normal bone marrow. The 50% reduction was chosen by analogy to the serum M-spike. We’ve recently analyzed an Eastern Cooperative Oncology Group study for the use of serum free light chain to predict hematologic response.
And the receiver operator curves indicated that the best cutoff for indicating hematologic response was a 45% change in the free light chain concentration, thus validating the use of a 50% reduction for partial response.
In summary, the current guidelines for disease monitoring suggest: use serum and urine electrophoresis if there are measurable M-spikes, that is, >1g/dL in serum and >200 mg/24 hour in urine. And, if you use quantitive serum Ig for large M-spikes, remember that they should correlate with the M-spikes, but are not equivalent. In addition, if there is no measurable M-spike in serum or urine, use the serum free light chain quantitation if the free light chain ratio is abnormal and the monoclonal free light chain is >10 mg/dL.