P-200: Pomalidomide-based chemotherapy in plasmacytoma at relapse

Background Plasmacytoma at the time of relapse of multiple myeloma is associated with poor response and survival. However, data on the activity of the recently available new drug or drug combinations in RRMM with plasmacytoma in the real-world clinical practice is limited. Pomalidomide and dexamethasone (Pd) with or without cyclophosphamide is an active therapeutic combination in relapsed and refractory multiple myeloma (RRMM) after 2 lines of previous line of therapy Method This study aimed to analyze the clinical outcome of the pomalidomide-based regimen in RRMM with plasmacytoma. Clinical data of 221 patients who were treated with Pd with or without cyclophosphamide from 7 hospitals participating in the Korean multiple myeloma working party were retrospectively analyzed by electronic medical chart review. All the of patients were previously treated with at least 2 lines of therapies including bortezomib and lenalidomide in most of the patients. Plasmacytoma was diagnosed by the computed tomography, magnetic resonance imaging or FDG-PET scan Result Twenty-nine patients among the 221 patients analyzed (13.1%) had plasmacytoma at the time of pomalidomide-based chemotherapy. Patients were previously treated with a median 4 lines of therapy (range, 2-14), including bortezomib, lenalidomide, autologous stem cell transplantation in 97%,100%, and 52% of the patients, respectively. 14 patients were treated with Pd and 15 patients had been treated with Pd and cyclophosphamide (PCd). Median number of sites of plasmacytoma involvement was 2 (range, 1-9), including paraskeletal and soft tissue involvement in 83% and 52% of the patients. Sites of soft tissue involvement were: 5 pleura, 4 lymph nodes, 4 subcutaneous, 3 liver, 3 muscle, 2 pancreas, 1 kidney, 1 pericardium, 1 peritoneum, 1 adrenal gland, and 1 stomach. 50% patients (13 among the 26 response evaluable patients) had responded to Pd with or without Cy: 2 complete response, 2 very good partial response, 9 partial response, 1 stable disease, 2 minimal response, and 10 progressive disease. Patients who were treated with PCd showed a better response compared with Pd therapy (53% versus 29%, P=0.264). After a median follow-up of 9.33 months (range, 0.30-52months), patients with plasmacytoma versus no plasmacytoma showed a progression-free survival of 3.57 (95% CI, 0.35-6.78 months) versus 8.40 months (95% CI, 7.00-9.80 months) (P=0.002) and an overall survival of 3.33 (95% CI, 0.00-7.82 months) versus 19.67 months (95% CI, 13.39-25.95 months) (P=0.001). Conclusion RRMM patients with plasmacytoma was responsive after pomalidomide-based chemotherapies. The addition of cyclophosphamide to Pd seemed to result in a better response compared with Pd only. However, RRMM patients with plasmacytoma had poorer survival compared with patients without plasmacytoma even after Pd with or without cyclophosphamide.