Real-World Evidence of Daratumumab Monotherapy in Relapsed/Refractory Multiple Myeloma Patients and Efficacy on Soft-Tissue Plasmacytomas

Introduction: Daratumumab is an anti-CD38 agent that was first investigated as single agent in GEN501 and SIRIUS trials in patients with advanced multiple myeloma (MM). Overall response rate (ORR) was 30% with positive impact on progression-free survival (PFS). However, there is a lack of information regarding plasmacytoma response. Materials and Methods: Here, we described a heavily pretreated group of 43 patients who received daratumumab monotherapy after EMA approval and focused on plasmacytoma response. Results: After a median follow-up of 26 months, median time to best response was 2.9 months (range 0.8-13.1), median PFS was 5.2 months (95% CI 2.5 ??? 8.8) and median OS was 11.2 months (95% CI 6.3 ??? 17.0). Patients who achieved at least partial response had longer median PFS and OS (12.8 and 20.2 months, respectively) than those who achieved minimal response or stable disease (5.3 and 11.2 months, respectively). Ten patients (23%) had plasmacytomas (70% paraskeletal, 30% extramedullary). The clinical benefit for patients with and without plasmacytomas was 20% versus 42%. A dissociation between serological and plasmacytoma response was observed in 40% of the patients. Thus, 50% of the patients with plasmacytomas achieved at least serological minimal response but only 20% had plasmacytoma response. Conclusion: This is the first real-world study of daratumumab monotherapy that focuses on efficacy data regarding soft-tissue plasmacytomas in patients with relapsed/refractory mieloma, showing a limited benefit in this patient population.