P-142: Stem cell collection after isatuximab or elotuzumab plus lenalidomide, bortezomib and dexamethasone in transplant-eligible multiple myeloma: single center data from the GMMG-HD6 and -HD7 trials

Introduction: In transplant-eligible patients with newly diagnosed multiple myeloma (MM), induction therapy followed by high-dose chemotherapy (HDCT) and peripheral blood stem cell (PBSC) transplantation is standard-of-care. Modern triplet and quadruplet regimen are commonly used as induction therapy, but their impact on PBSC mobilization and collection outcomes remain incompletely understood.
This study evaluates the impact of prolonged lenalidomide induction and isatuximab- or elotuzumab-containing quadruplet induction therapies on PBSC mobilization and collection.

Methods: 179 transplant-eligible patients with newly diagnosed MM treated within the randomized phase III clinical trials GMMG-HD6 (NCT02495922) and GMMG-HD7 (NCT03617731) at a single academic center were included. The median age at diagnosis was 59 (range 26-71). 62% of patients were male, 65% showed IgG myeloma, 64% kappa light chain restriction, and 28% presented with high-risk cytogenetics. Patients were evaluated according to PBSC mobilization and collection parameters such as overall collection result, CD34+ cell levels in peripheral blood, leukapheresis (LP) delays and overall number of LP sessions as well as the rate of rescue mobilization with plerixafor. Patients underwent four different induction regimen: Lenalidomide, bortezomib, and dexamethasone (RVd, six 21-day cycles, n=44), isatuximab-RVd (six 21-day cycles, n=35), RVd (four 21-day cycles, n=51), or elotuzumab-RVd (four 21-day cycles, n=49).

Results: Patients’ characteristics were well balanced among groups. Collection failures, defined by the inability to collect three sufficient PBSC transplants, were rare (n=3, 2%) with no occurence in the isatuximab-RVd and elotuzumab-RVd groups. Intensified induction with six 21-day cycles of RVd in comparison to four 21-day cycles of RVd did not hamper overall numbers of collected PBSC (9.7 x106/kg bw, IQR 3.1, versus 10.5 x106/kg bw, IQR 3.9, p=0.331). Plerixafor was more commonly used after six cycles versus four cycles of RVd (16% versus 8%). No negative impact on overall PBSC collection was observed upon addition of elotuzumab to RVd (10.9 x106/kg bw, IQR 3.8 versus 10.5 x106/kg bw, IQR 3.9, p=0.915). Patients treated with isatuximab-RVd (six cycles) had overall lower numbers of collected stem cells as compared to patients receiving RVd (six cycles) induction (8.8 x106/kg bw, IQR 1.8 versus 9.7 x106/kg bw, IQR 3.1, p=0.801), without experiencing more LP delay or significantly increased numbers of LP sessions in a multivariable logistic regression analysis. Plerixafor use was more common after isatuximab plus RVd versus RVd alone (34% versus 16%).

Conclusions: We provide the first detailed data on stem cell collection after induction with isatuximab plus RVd. These data demonstrate that stem cell collection is feasible after prolonged induction with isatuximab-RVd without collection failures. Addition of elotuzumab to RVD as well as prolonged induction with RVd did not affect stem cell yield.