Phase 1/2 Trial Of Lenalidomide In Combination With Cyclophosphamide and Prednisone (REP) In Patients With Lenalidomide-Refractory Multiple Myeloma (REPEAT-study)

The outcome of multiple myeloma (MM) patients who are no longer responding to thalidomide, lenalidomide (LEN) and bortezomib (BORT) is very poor, with a median event-free survival of 5 months and median overall survival (OS) of 9 months (Kumar SK et al, Leukemia 2012; 26;149-157). We have previously shown in a small retrospective study that the combination of continuous low dose oral cyclophosphamide (endoxan) and prednisone combined with lenalidomide (REP) had remarkable activity in heavily pretreated LEN-refractory multiple myeloma patients (median 6 lines of previous chemotherapy) (vd Donk et al; Br J Haematol 2010;148(2):335-7). To determine the optimal dose of lenalidomide with continuous cyclophosphamide and prednisone, we initiated a prospective study to evaluate the maximum tolerated dose (MTD) of the REP regimen and to assess its efficacy and safety in LEN-refractory MM patients. Here we report safety and efficacy data from the phase 1 dose-escalation part of the REPEAT-study (NCT01352338).

Patients aged ≥ 18 years with LEN-refractory MM, ECOG-performance status 0-3 and adequate kidney, liver and hematologic function were included. Five dose levels were evaluated using a standard 3+3 design, based on dose-limiting toxicities (DLTs) occurring in cycle 1. Patients received LEN in doses ranging from 10-25 mg/day on days 1-21 of 28-day cycle, while oral cyclophosphamide (50 or 100 mg) and prednisone (20 mg) were given continuously. Therapy was continued until progression. The MTD for the phase 2 part is defined as the highest dose level with 0 or 1 DLT's observed in 6 patients.

Up till now, 35 patients were enrolled (22 in phase 1 and 13 in phase 2) from August 2011 to June 2013. The phase 2 part is still recruiting and data are not evaluable yet. One patient in phase 1 was excluded because of study violation and is not included in the analysis. The median age of the 21 evaluable patients in phase 1 was 69 years (range 41-73); 76% were male. The median duration of the disease from diagnosis was 41 months (range 18-96), median number of prior therapies was 3 (range 2-6), and 12 patients (57%) had previously received autologous SCT. All patients were LEN-refractory, 19 (90%) had prior BORT treatment, and 16 (76%) had BORT-refractory MM. Fifty-five % of the patients were considered high risk by FISH. At the time of analysis, 16 of 21 patients in phase 1 have discontinued treatment because of disease progression (13), alternative treatment (allo-SCT) (1), or adverse events (2). The MTD was defined as LEN 25 mg days 1-21 of a 28-day cycle, combined with oral cyclophosphamide 50 mg and prednisone 20 mg continuously (dose level 4), based on three patients experiencing a DLT: two developed pneumonia (in dose levels 4 and 5; CTC grade 3), and one patient at dose level 5 experienced CTC grade 3 dyspnea. Neutropenia (18%) and thrombocytopenia (18%) were the most common grade 3 hematological adverse events (AEs), which were managed with growth factor support and/or dose modification. There were no grade 4 hematologic AEs. Grade 3 respiratory tract infections (29%) and grade 2 fatigue (19%) were the most common non-hematological AEs. Venous thromboembolism occurred in 1 patient.

Figure 1 shows a waterfall plot of the responses of the patients that participated in the phase 1 part of the study. Overall response rate (≥ PR) was 67% with 6 out of 21 (29%) patients achieving at least VGPR. In addition 2 patients achieved MR (≥ MR: 76%). Median PFS and OS were 6.3 and 15.5 months respectively. Similar results were achieved in the subset of patients with LEN- and BORT-refractory disease. Interestingly, laboratory experiments with purified myeloma cells from these patients suggest synergism between LEN and cyclophosphamide.

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The REP regimen induces high response rates and prolonged PFS and OS in LEN-refractory patients with acceptable toxicity. The MTD is defined as LEN 25 mg days 1-21 of a 28-day cycle, combined with oral cyclophosphamide 50 mg and prednisone 20 mg continuously. Phase 2 is enrolling patients and evaluates efficacy and safety of the REP regimen at the MTD. REP should be considered a valuable salvage option for LEN-refractory MM patients. We will present an updated follow-up at ASH.

Sonneveld:Onyx: Research Funding; Millenium: Research Funding; Janssen-Cilag: Research Funding; Onyx: Honoraria; Celgene: Honoraria; Janssen-Cilag: Honoraria; Celgene: Research Funding. Lokhorst:Genmab A/S: Consultancy, Research Funding; Celgene: Honoraria; Johnson-Cilag: Honoraria; Mudipharma: Honoraria. van de Donk:Celgene: Research Funding.