A Multicenter Open Label Phase II Study of Pomalidomide, Cyclophosphamide and Dexamethasone in Relapse Multiple Myeloma Patients Initially Treated with Lenalidomide, Bortezomib and Dexamethasone

Introduction: The rate of response (partial remission and better) to pomalidomide and low dose dexamethasone in myeloma patients who had previously received lenalidomide and bortezomib was 33% (Richardson PG, et al. Blood 2014;123:1826). In view of improving the response rate of pomalidomide based therapy, we conducted a phase II trial to evaluate the efficacy and safety of the addition of weekly oral cyclophosphamide to pomalidomide and dexamethasone (PCD) in patients in first relapse following initial treatment in the IFM 2009/DFCI trial (Attal M, et al. NEJM 2017;376:1311). Since the combination of lenalidomide, bortezomib and dexamethasone (RVD) is becoming the standard of care in the frontline setting with or without autologous stem cell transplantation (ASCT), our goal was also to find an effective salvage regimen to induce new remission in patients relapsing after exposure to lenalidomide and bortezomib so as to be able to proceed to ASCT (ClinicalTrials.gov identifier: NCT02244125).

Patients / Methods: Eligible patients had relapsed myeloma after one line of treatment according to the IFM 2009/DFCI trial. All patients had received RVD as induction and consolidation therapy plus lenalidomide maintenance for 1 year (Arm A). Half of them had undergone upfront ASCT after the induction phase as part of the initial protocol (Arm B). At first relapse, all patients received oral pomalidomide 4 mg on D1-21, oral cyclophosphamide 300 mg on D1, 8, 15 and 22 and oral dexamethasone 40 mg D1-4 and D15-18 of a 28 day cycle (PCD). Four reinduction cycles were administered to all patients. Those who had not been transplanted initially (Arm A) and who were responding underwent ASCT and received two additional cycles of PCD while those who had already been transplanted (Arm B) received 5 cycles of PCD. All were subsequently treated with pomalidomide plus dexamethasone maintenance until disease progression. The primary endpoint was the rate of partial response or better after the initial 4 cycles of PCD. Responses were assessed using the IMWG criteria.

Results: Between April 2014 and February 2017, 100 patients were enrolled. The cut-off date for this intermediate analysis was 4^th July 2017. At inclusion in the relapse trial, the median age was 62 years (range 39-70), and 62% of the patients were male. The median time from diagnosis of myeloma to current therapy was 3.6 years (3.1-4.3, 1^st and 3^rd quartile) and 97% had a PS of 0 or 1. The myeloma isotype was IgG (72%), IgA (17%), light chain (9%) or IgD (2%). Five patients had a plasmacytoma and 15% high risk cytogenetics (t(4-14) and/or del 17p and/or t(14-16)). The ISS was I (78%), II (15%) or III (7%).

In 90 evaluated patients after 4 cycles of PCD, objective responses were obtained in 82 (91%): CR: 2 (2.2%), VGPR: 29 (32%) and PR: 51 (57%). Stable disease was observed in 3 patients (3%) and progressive disease in 5 (5.6%). Adverse events (AE) of grade 3-4 occurred in 72 patients (72%) including hematological toxicities (61%) (53% neutropenia, 36% lymphopenia, 6% anemia, 5% thrombocytopenia), infection (8%) (63% pneumonia), asthenia (7%), hyperglycemia (6%), gastrointestinal disorders (3%), allergic skin reactions (2%) and cardiovascular disorders (3%) (1 pulmonary embolism, 1 myocardial infarction and 1 syncope). There was no grade 3 or 4 peripheral neuropathy. Six patients (6%) discontinued one of the study drugs (P, C or D). Dose reductions were recorded in 38% of the patients for pomalidomide, in 35% for cyclophosphamide and in 46% for dexamethasone, the reasons being AE/SAE (77%, 70% and 71%), omission (13%, 13% and 9%) and other (10%, 17% and 20%) (P, C and D, respectively). Four of the 50 patients in Arm A could not have the planned ASCT at relapse while 7 of the 50 in Arm B received a second ASCT. PFS (PFS1 and PFS2) and OS will be reported during the meeting.

Conclusion: In this first planned relapse trial, the all oral combination of pomalidomide, cyclophosphamide and dexamethasone was very efficacious at first relapse following lenalidomide, bortezomib and dexamethasone treatment. After 4 cycles, the rate of partial response or better was 91% and 92% of the patients could proceed to ASCT. Toxicity was mostly hematological and manageable. These results should be compared to those of other pomalidomide and dexamethasone-based second line therapies.