Host and Disease Factors Impacting Presence of Accessory Band during Therapy with Daratumumab in Multiple Myeloma Patients

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Achieving and maintaining Complete Response (CR) after autologous hematopoietic cell transplant is the key to improved clinical outcomes in patients (pts) with multiple myeloma (MM). Daratumumab (DARA), an IgG1 Kappa anti-CD38 monoclonal antibody, have shown significant anti-myeloma activity leading to increasing usage in the peri-transplant settings. Frequently, use of DARA may be associated with appearance of low concentration band on serum protein electrophoresis (SPE) impacting CR assessment after transplant. The incidence and factors influencing appearance of this band are largely unknown. This band potentially can be an indirect measurement of the plasma DARA concentration influenced by amount of administered agent and but also with volume of CD38 positive myeloma cells binding to DARA. The objective of this study is to analyze the factors influencing appearance of this band on SPE. Methods: 77 pts who received DARA were retrospectively studied. Pts who did not have available SPE after starting DARA (n: 9) and those who had AL Amyloidosis without Myeloma (n: 3) were excluded. The host and disease characteristics extracted. Pts assigned to two cohorts based on presence (PB) or absence (NB) of the accessory band. The disease response assessment was assessed based on IMWG criteria. Result: Median age for pts in PB and NB was 62 and 64.4 years respectively. All pts received weight-based dosing (16mg/Kg). 31 pts had detectable band assigned to PB cohort and 34 pts without any detectable band assigned to NB. The accessory band appeared over a median of 46 days after starting therapy (range: 7-390 days) and predominantly (74%) during the weekly DARA schedule. No significant difference noted in median weight and serum creatinine between PB and NB cohorts. Median M-spike on SPE at the start of DARA was 1.1 gr/dL (range: 0 - 5.5 gr/dL) in NB cohort vs. 0.3 gr/dL (range: 0 3.8 gr/dL) in PB patients (p-value Conclusion: Based on our data, the frequency of detecting this band is not impacted by type of myeloma (i.e., IgG vs. IgA) but by the magnitude of the M-spike. This may be reflective of larger disease volume in bone marrow with less M protein detected in the peripheral blood. The appearance of accessory band associated with DARA treatment during weekly dosing may be a surrogate early marker for predicting disease response. Further large scale studies are required to confirm this findings.