Impact of M-protein detection on the response evaluations of patients undergoing treatment with the IgG-κ monoclonal antibodies daratumumab or isatuximab, and discrepancies between immunofixation electrophoresis (IFE) systems and reagents.

BACKGROUND: Immunofixation electrophoresis (IFE) is the standard method for confirming the presence of a monoclonal protein (M-protein) at multiple myeloma (MM) diagnosis. IFE is also essential at assessment of complete response (CR) and stringent CR during treatment. As the CR assessment is influenced by daratumumab and isatuximab, HYDRASHIFT assays were developed. METHODS: Samples from patients under treatment that included daratumumab or isatuximab were tested and monitored by IFE on the HYDRASYS system using HYDRASHIFT assays (HYDRASYS/HYDRASHIFT) and by IFE on the Epalyzer2 system (Epalyzer). RESULTS: The IFE using HYDRASYS/HYDRASHIFT avoided a false positive caused by drug-related IgG-κ and contributed to accurate assessment of CR. Furthermore, HYDRASYS/HYDRASHIFT detected small M-proteins at early relapse and detected free light chains (FLCs) in patients with renal impairment exhibiting high serum FLCs despite being often missed on Epalyzer. CONCLUSION: Sensitivity and specificity of M-protein detection vary greatly depending on the IFE system and reagents used.