Evaluation of Stem Cell Mobilization in Patients with Multiple Myeloma after Lenalidomide-Based Induction Chemotherapy within the GMMG-HD6 Trial

Introduction: The German-Speaking Myeloma Multicenter Group (GMMG) has initiated a randomized multicenter phase III trial on the effect of elotuzumab in VRD (bortezomib, lenalidomide, dexamethasone) induction/consolidation and lenalidomide maintenance in patients with newly diagnosed multiple myeloma (GMMG-HD6 trial, NCT02495922). The study compares four cycles induction therapy with VRD vs. VRD + elotuzumab, followed by standard intensification (i.e. mobilization and stem cell transplantation), two cycles consolidation with VRD/VRD + elotuzumab and lenalidomide maintenance +/- elotuzumab. The primary endpoint is determination of the best of four treatment strategies regarding progression-free survival. Here we present a first analysis of stem cell mobilization within this study.

Patients and Methods: We performed a retrospective analysis of collection data on all patients who underwent peripheral blood stem cell (PBSC) collection between trial initiation in June 2015 and June 2016. Only patients with completely available datasets in respect of mobilization were considered (n=111). The vast majority of 99 patients (89%) received chemomobilization with CAD (cyclophosphamide, adriamycin, dexamethasone) followed by 5-10 µg G-CSF /kg body weight (bw) /d (starting day +9 until completion of PBSC collection), while in one case (1%) dexamethasone was omitted and in 10 cases (9%) cyclophosphamide mono was administered. One patient underwent steady-state mobilization with G-CSF only (10µg /kg bw /d). 55/111 patients received VRD (50%), whereas the remaining patients received VRD + elotuzumab. According to the recommendations of the study group, PBSCs for three stem cell transplants were to be collected. One transplant ideally consisted of ≥2.5 x10^6 CD34+ cells /kg bw, but in the event of poor mobilization as low as ≥2.0 x10^6 CD34+ cells /kg bw would be considered acceptable.

Results: The median number of collected CD34+ cells was 10.4 x10^6 /kg bw (range 2.88 to 23.01 x10^6 /kg bw). Overall, 92 patients (83%) collected ≥7.5 x10^6 CD34+ cells /kg bw and another 12 patients (11%) collected between 6.0 and 7.5 x10^6 CD34+ cells /kg bw, resulting in three transplants, respectively. Only 7 patients (6%) collected below 6.0 x10^6 CD34+ cells /kg bw; 5 of them had been treated in the VRD-arm without elotuzumab. Due to insufficient PBSC mobilization after conventional treatment, 14 patients (13%) received a rescue mobilization with plerixafor, from which 12 patients collected ≥6.0 x10^6 CD34+ cells /kg bw. Overall, 7 serious adverse events (SAEs) occurred during mobilization phase, 4 of them in the study arm with elotuzumab.

Conclusions: Cyclophosphamide-based chemomobilization after induction therapy with VRD is feasible. Efficient PBSC collection of ≥6.0 x10^6 CD34+ cells /kg bw could be performed in 104 of 111 patients (94%), with a low incidence of SAEs. The need for rescue mobilization was not higher than that of comparable previous GMMG treatment protocols. The addition of elotuzumab during induction phase did not impede PBSC collection.