Phase 3 Study of Pomalidomide with Cyclophosphamide and Dexamethasone Versus Pomalidomide and Dexamethasone in Asian Patients with Relapsed/Refractory Myeloma (RRMM) - Interim Analysis of a Trial By the Asian Myeloma Network (AMN)

Abstract

Background Pomalidomide is an immunomodulatory drug that has been approved for the treatment of relapse refractory myeloma. A previous small randomized phase 2 study in the United States showed that combination of Pomalidomide, cyclophosphamide and dexamethasone induce a greater response rate than pomalidomide and dexamethasone1. In our prior study, AMN0012, we should that in patients with sub-optimal response to pomalidomide and dexamethasone, the addition of cyclophosphamide can increase response resulting in improvement of progression free survival. In the current study, we seek to randomize Asian patients with RRMM between PCD and PD to confirm the benefit of PCD. Method We conducted a prospective randomized trial of pomalidomide (4mg daily for 21 days followed by 7 days rest) plus dexamethasone 40mg once weekly for 4 weeks with or without cyclophosphamide (400mg once a week) in patients with relapse and refractory myeloma that has to be refractory to lenalidomide and has prior exposure to proteasome inhibitors. Each cycle is 4 weeks. Patients from Singapore, Japan and Korea (NCT03143049) were included in this Asian Myeloma Network trial. The trial was started in Sep 2017 and is still ongoing. To date, 53 patients have been recruited so far. This interim report presents data available up till the data cut-off date of 24 June 2020. Results Forty-six patients have available base line information and safety data and is included in this interim analysis. 50% of patients are male and median age of the cohort is 68 years old. 39% and 28% of patients are International Stage System (ISS) stage 2 and 3 respectively. 20% of patients have abnormal creatinine clearance. Median prior line of treatment is 3. All patients are refractory to lenalidomide and 96% have prior exposure to bortezomib. In addition, 12 patients (26%) and 5 (11%) have been treated with Carfilzomib and Ixazomib respectively. 15 (33%) patients had prior high dose melphalan and autologous stem cell transplant. 20 (44%) patients required dose reduction of pomalidomide, cyclophosphamide or dexamethasone. 89% of patients experience adverse events (AEs) of any grade. Of the 297 episodes of AEs, 43% are grade 3 or higher, with 50% of these episodes related to the study drugs. 57% of patients experienced serious AEs (SAEs) of any grade. Of the 74 episodes of SAE, 89% are grade 3 or higher, with 49% of these episodes related to the study drugs. Almost all of these events are related to cytopenias and infections. 20 (44%) of the patients develop grade 3 neutropenic fever and 9 (20%) patients have grade 3 or higher pneumonia. Only 1 patient experienced grade 3 peripheral neuropathy, 1 patient develop grade 3 pulmonary embolism, 1 patient developed grade 3 venous thromboembolism, and 1 patient experienced grade 3 renal impairment. At a median follow-up of 10.9 months, 9 of the 46 patients have died, and 21 have progressed. Three patients withdrew due to toxicity. While the overall response of the study population is not part of this interim analysis, we assessed the response of patients from the National University Cancer Institute, Singapore which has the highest number of patients recruited to get an idea of the therapeutic efficacy. Of the 14 patients recruited at NCIS, 1 patient achieved CR, 3 VGPR, 7 PR, producing a response rate of 79%. Conclusion In this interim analysis of a prospective randomized study of pomalidomide and dexamethasone with or without cyclophosphamide in Asian patients, we demonstrated the feasibility and efficacy of this combination. Longer follow-up and final analysis of the study will be needed to ascertain the therapeutic advantage of PCD over PD in relapse and refractory myeloma that is refractory to lenalidomide.