P-360: IMPACT OF DARATUMUMAB/BORTEZOMIB/THALIDOMIDE/DEXAMETHASONE (DVTD) INDUCTION THERAPY ON CHEMO-FREE STEM CELL MOBILIZATION IN NEWLY DIAGNOSED MULTIPLE MYELOMA PATIENTS: A REAL LIFE EXPERIENCE

Introduction: Daratumumab-based induction followed by autologous stem cell transplantation (ASCT), is the standard of care for transplant-eligible newly diagnosed multiple myeloma patients (NDMM). Daratumumab (Dara) adversely affects stem cell mobilization, and this is clearly reported in prospective clinical trials. Here, we described a real-life experience on peripheral blood stem cell (PBSC) mobilization in patients treated with Dara-based induction.

Methods: From 2022 to 2024, NDMM patients treated with Dara, bortezomib, thalidomide and dexa (DVTD) were mobilized using G-CSF 10 µg/kg/day, in 2 centres. PBSC minimum target was 2.5x10⁶ cells/kg for 1 ASCT and 5x10⁶ cells/kg for 2 ASCT. Plerixafor (Plx) 240 µg/kg was used on demand when circulating CD34+ was less than 20/µL at day +5. Categorical variables were reported as count with percentage and continuous variables as median with range. Chi-square tests were used to compare categorical variables and p value < .05 was considered for statistical significance.

Results: 100 patients were included. Median age was 61 years (range 42-71). Median induction cycles were 4 (3-6); 63% of patients mobilized after fourth cycles, 37% after third cycle; median time from last Dara to G-CSF start was 25 days (9-109). Responses to induction were: CR 16%, VGPR 60%, PR 16%, SD 1%. PBSC mobilization was successful in 90% of cases. Plx was added in 36%. The median CD34+ peak was 39/µL (0-490); the median of CD34+ cells harvested was 6.7x10⁶/kg (2.5-23.9) with 66% of patients harvesting more than 5×10⁶/kg. The median number of apheresis was 1.7 (range 1-3). 10 patients failed first mobilization, and 9/10 were subsequently mobilized with chemo-based regimen. In univariate analysis, age ( >60y vs < 60y), response after induction (≥VGPR vs < VGPR) and days from last Dara ( >25 vs < 25) did not affect Plx use and number of apheresis. The number of apheresis’ day was longer in pts mobilized after 4 vs 3 induction cycles (p=0.049). All patients received ASCT. The median time to absolute neutrophils count >0.5 and platelets count more than 20 was 11 (6-24) and 13 days (7-30) respectively.

Conclusions: our study showed that chemo-free PBSC mobilization is feasible and effective even after DVTD induction. However, the use of Plx seems to be higher. 10% of patients failed to mobilize, and a second round of mobilization was effective for harvesting stem cells.