COMy 2026 | How is the role of sFLC evolving for assessing disease response in myeloma?

We’re here at the COMy meeting and we’ve already had several exciting sessions. I spoke on the role of serum-free light chains and the role of urine in our new response criteria which will be published very soon. I think the collection of 24-hour urine for response assessment has been an increasing burden and in fact many units have stopped doing it. Indeed, I think it’s only required now for diagnosis in order to confirm the presence of Bence Jones protein in the urine, and for confirmation of complete response, or CR, because you need to be immunofixation negative in the urine, and a spot urine is not really good enough because of the variability in protein excretion. So you need a full 24-hour urine collection, and then that needs to be concentrated in order for the urine electrophoresis and immunofixation. I think outside those requirements, probably urine 24-hour Bence Jones protein is not required, strictly speaking, for disease response and assessment. Now, the situation is quite different in precursor disease because we have some recent data published a couple of years ago that for patients with precursor disease and high serum-free light chains, the cutoff of a serum-free light chain ratio of 100 to designate a biomarker of malignancy is probably a little low, and we can distinguish those patients based on their urine protein excretion. So then you still need to measure a 24-hour urine excretion of Bence Jones protein and the cutoff is 200 milligrams per 24 hours. If you have an excretion more than 200 milligrams per 24 hours, then your chance, your risk of developing myeloma is far greater. So those are the situations in which I think it’s important still to measure 24-hour urine excretion with Bence Jones protein. For the serum-free light chains, we have some new response, we have some new reference ranges, and these have been largely drawn up, validated by the iSTOP Iceland group, in which they looked at which they developed new reference ranges based on renal clearance, based on renal function, and also based on age, age 70 and below, or age 70 and above. So I think we are looking at a new era where we will use serum-free light chains increasingly, and we will use them ahead of 24-hour Bence Jones protein for disease measurement. But we will also have new reference ranges to use. And I think the use of 24-hour urine collection for Bence Jones protein will increasingly be more focused on certain situations.

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