ANNALS EXPRESS: Implications for the monitoring of patients with multiple myeloma during treatment with the immunotherapy daratumumab.

Background The novel daratumumab immunotherapy is a human IgG1 kappa antibody targeted against CD38, which is almost universally expressed on myeloma plasma cells. Daratumumab has efficacy in clinical trials for the treatment of multiple myeloma; however, it complicates laboratory monitoring of the serological response to treatment, as it is detected by serum electrophoresis and/or immunofixation. Methods Laboratory reports of electrophoresis patterns serially performed in a single laboratory of six patients with relapsed multiple myeloma receiving daratumumab therapy as part a clinical trial were reviewed retrospectively. Results Post administration of daratumumab therapy, an additional band was visible by serum electrophoresis, migrating to the mid-gamma region, which was confirmed as IgG kappa by immunofixation. In five out of the six patients, this band was quantified at <2.0 g/L. For one patient, this band co-migrated with the patient's disease paraprotein band, so both bands were quantified together. The appearance of an apparent second paraprotein band while receiving treatment for multiple myeloma can cause anxiety for patients, confusion for healthcare workers and may also underestimate complete remission rates. Conclusions The clinical laboratory must be aware of the interference of daratumumab in serum electrophoresis. Effective communication between clinicians and the laboratory is essential for the production of clinically valuable, non-misleading reports for these patients.