Pomalidomide, Cyclophosphamide, and Dexamethasone Is Superior to Pomalidomide and Dexamethasone in Relapsed and Refractory Myeloma: Results of a Multicenter Randomized Phase II Study

Background: Pomalidomide-dexamethasone results in an overall response rate of 33% and median PFS of 4.2 months in patients with prior lenalidomide and bortezomib (Richardson et al. Blood 2014). In this randomized phase II trial, we compared pomalidomide-dexamethasone (arm B) versus the addition of oral weekly cyclophosphamide to pomalidomide-dexamethasone (arm C) in patients with lenalidomide-refractory multiple myeloma (MM). We have previously reported that the recommended phase II dose of cyclophosphamide with standard-dose pomalidomide + dexamethasone was 400 mg PO D1, 8, 15.

Patients and Methods: Eligible patients had relapsed and refractory MM after at least 2 prior therapies and were lenalidomide refractory. Patients had a platelet count ≥ 50,000/mm³ and ANC ≥ 1,000/mm³ (patients with ≥50% bone marrow plasmacytosis were allowed if platelet count was ≥ 30,000/mm³and ANC could be supported with GCSF during screening and therapy). Patients were randomized (1:1) to receive pomalidomide 4 mg PO D1-21 and dexamethasone 40 mg PO D1, 8, 15, 22 (20 mg if older than 75 years) (arm B) with or without oral cyclophosphamide 400 mg PO D1, 8, 15 of a 28-day cycle (arm C). Patients randomized to arm B were allowed to cross over to arm C in the event of disease progression. Thromboprophylaxis was mandated with aspirin, warfarin, or LMWH. The primary endpoint was overall response rate using IMWG criteria. Secondary endpoints included an evaluation of PFS, OS and safety of the two arms.

Results: Between 7/2012 and 3/2014, 36 patients were randomized to arm B and 34 to arm C. Patients characteristics were not different between the 2 arms (table below). The median number of prior therapies was 4 (2-12). All patients were lenalidomide refractory and none received prior pomalidomide. After a median follow up of 15 months, the overall response rate (partial response or better) was 39% and 65% (p=0.03) for arm B and C, respectively. The clinical benefit rate (minimal response or better) was 64% and 79% (p=0.2) for arm B and C, respectively. The median PFS was 4.4 months (95% CI 2.3-5.9) for arm B and 9.2 months (95% CI 4.6-16) for arm C (log rank p=0.04). As of July 2014, 28 patients had died (16 arm B, 12 arm C) with median overall survival of 10.5 versus 16.4 months (p=0.08) for arm B and C, respectively. Hematologic grade 3/4 adverse events were more frequent in arm C, although this was not statistically significant (see table). Thirteen patients crossed over and oral weekly cyclophosphamide was added to their tolerated dose of pomalidomide dexamethasone. For those patients, the best response was as follows: 2 PR, 2 MR, and 6 SD, 3 PD.

Conclusions: Pomalidomide-dexamethasone in combination with oral weekly cyclophosphamide resulted in a superior response rate and PFS compared to pomalidomide-dexamethasone alone in patients with relapsed and refractory MM. The increased hematologic toxicities, as a result of the addition of oral cyclophosphamide, were manageable.