Lenalidomide/Rituximab Maintenance After Induction With Fludarabine/Rituximab In Combination With Escalating Doses Of Lenalidomide In Previously Untreated Chronic Lymphocytic Leukemia (CLL): The Revlirit CLL5 AGMT Phase I/II Study, Final Results

Lenalidomide has shown encouraging activity in monotherapy trials in CLL, but tumor lysis and tumor flare presented obstacles in development. We and others previously presented first data on combinations of lenalidomide with standard treatment regimens in CLL. As reported at ASH 2011 we combined Lenalidomide safely and efficaciously with the combination of Fludarabine and Rituximab, achieving early reduction of tumor load without tumor lysis or tumor flare and with high response rates. We also uncovered a patient population unable to tolerate higher Lenalidomide doses and marked by an exhausted T cell subset, measured pre-treatment. We now report final results of this trial, including the maintenance phase.

In induction Lenalidomide was combined with Fludarabine (40mg/m² po d1-3 q28d) and Rituximab (375mg/m² iv d4 cycle 1; 500mg/m² iv d1 cycles 2-6, q28d). In cycle 1 Lenalidomide was added day 7-21 at 2.5 mg. Toxicity permitting, Lenalidomide dose was escalated to 5, 10, 15, 20 and 25mg day 1-21 over cycles 2-6. Subsequent maintenance treatment was two-monthly Rituximab at 375mg/m² and Lenalidomide at the last dose tolerated in combination in a 28 day cycle without interruption for 6 months. The main goal of this treatment phase was to establish safety and efficacy as a secondary endpoint to the study.

Patient characteristics of 45 recruited patients were previously reported: median age was 66 years and at least one molecular high risk feature was present in 64% of patients. No systematic toxicity determining an MTD in induction, the primary study endpoint, was found. The median daily dose in cycle 6 was 15mg in 40 evaluable patients, with 3 patients receiving the last cycle without lenalidomide. Toxicity and efficacy of the induction regimen were reported previously. Maintenance treatment was started in all 40 patients finishing induction. Three patients that finished without lenalidomide received only Rituximab. The median starting dose for all 40 patients was 15mg daily and 70% started with 10mg upwards. In total, 46% needed dose reductions, with prolonged neutropenia being the main reason, but 47% received doses above 10mg up to cycle 6 of maintenance. Interestingly, 9/13 patients receiving 25mg as maintenance were able to receive the treatment uninterrupted for 6 months, suggesting that a biologically select group may tolerate very high doses. As alluded to the major toxicity was neutropenia with 45% and 27% reaching G3 and G4, respectively. Surprisingly this did not translate into a relevant signal for infections. Grade 3, but no G4 infections, were observed in 5% of patients and all other G3/4 toxicities remained below 5%. Compared to the reported incidence of skin reactions in induction, we did not observe a significant signal in the maintenance phase. Improvement of response from PR after induction to CR at the end of maintenance was observed in 25%. The overall best response in ITT to the regimen during induction and maintenance was CR in 67% and PR in 29%. Median follow up of the study is now 35 months, at which point PFS is 89% and observed median PFS is currently 46 months. Exploratory analyses show no significant influences of age>65, mutation state or CD38 risk on PFS, but undetectable MRD after induction and high risk cytogenetics showed borderline effects (both p=0.08), the latter (2 cases with del17p and 9 with del11q) being driven by relapses in patients with del11q with a median PFS of 42 months in this group.

A combination of Lenalidomide with FR followed my maintenance with Lenalidomide and Rituximab proved clinically feasible. While initial dose-finding was complicated by highly individual levels of tolerance to lenalidomide in the combination (with skin toxicity being a major problem), the main toxicity in maintenance was neutropenia. Although the important myelotoxicity did not translate into a rate of infection above that expected after induction treatment, our judgment is, that a more moderate approach to dosing may be warranted in maintenance, since a majority of patients had to be dose-adjusted. Finally, the PFS observed with this induction and maintenance regimen seems encouraging by comparison with other first line regimens. While the exploratory nature of the trial clearly limits this conclusion, we further explore combination approaches with lenalidomide.

Egle:Celgene: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Roche: Honoraria, Research Funding. Off Label Use: Lenalidomide in CLL. Pleyer:Celgene: Honoraria, Research Funding. Fridrik:Roche: Honoraria. Thaler:Roche: Honoraria, Research Funding. Greil:Roche: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Research Funding.