Phase II Testing of Lenalidomide Plus Melphalan for Previously Untreated Older Patients with Multiple Myeloma: Toxicity Data from the NCIC CTG MY.11 Trial.

Introduction. The NCIC CTG is conducting phase II testing to establish the tolerability and estimate the efficacy of combining lenalidomide (L) + melphalan (M) over multiple cycles for previously untreated patients with multiple myeloma who are ineligible for stem cell transplantation. We report the data from the preliminary safety phase of this trial.

Methods. The MY.11 trial was initially designed as a randomized phase II test of M 9 mg/m² given on days 1–4 (M9) plus either L 10 mg (L10) or 20 mg given on days 1–21 of a 28 day cycle. Primary prophylaxis with G-CSF was not included, but use of G-CSF for established neutropenia was permitted; our intent was to determine dose levels that could be given independently of G-CSF. A dose attenuation schedule was developed for neutropenia and/or thrombocytopenia that was severe and occurred during the administration of L or was persistent and caused a delay in the next treatment cycle. A hematologic dose limiting toxicity (H-DLT) was defined as the need for 2 dose attenuations of L or 1 dose attenuation of M. Prior to the randomized phase of the trial, a safety run-in phase testing M9+L10 in 6 patients was planned; closure of this arm was to occur if, during the first 3 treatment cycles, there were ≥ 3 H-DLTs or any non-hematologic serious adverse event (SAE) judged to be treatment related. Four of the planned 6 patients were entered; during their first 3 treatment cycles, each experienced a H-DLT and one died from sepsis. The study was therefore amended with the intent to conduct a randomized phase II test of M 4 mg/m² days 1–4 plus L 15 mg days 1–21 (M4L15) and M 6 mg/m² days 1–4 plus L 10 mg days 1–21 (M6L10). Prior to the randomized phase of testing, each regimen was tested in non-randomized safety run-ins that included 6 patients per arm. The same parameters as above for study arm closure were applied. If the M6L10 arm was closed, the trial would proceed to test M 5 mg/m² days 1–4 and L 10 mg days 1–21 (M5L10).

Results. Six patients were enrolled to M4L15: during their first 3 treatment cycles, 4 patients experienced H-DLTs related to severe or persistent grade 3–4 neutropenia and one other patient experienced an SAE related to hallucinations and multiple constitutional complaints. This arm was therefore closed to accrual. Six patients were enrolled to M6L10: during their first 3 treatment cycles, 3 patients experienced H-DLTs related to severe or persistent grade 3–4 neutropenia. One of these patients was hospitalized with pulmonary edema and another with febrile neutropenia. This arm was therefore closed and the MY.11 trial amended to proceed as a single-arm phase II testing M5L10.

Conclusion. Although M + L holds promise as an effective combination for previously untreated myeloma patients, the regimen is associated with considerable myelosuppression. The efficacy of the combination when given at tolerable doses remains to be established.