P27 HIGH DOSE CYCLOPHOSPHAMIDE AS MOBILIZATION REGIMEN IN NEWLY DIAGNOSED MULTIPLE MYELOMA: SAFETY AND EFFICACY IN AN OUTPATIENT SETTING. SINGLE CENTER EXPERIENCE

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Background and aim of the study: High-dose chemotherapy followed by autologous stem-cells transplantation (ASCT) is the standard treatment approach in eligible newly diagnosed multiple myeloma (MM) patients. The use of Daratumumab in frontline therapy seems to affect stem cell mobilization and engraftment with lower number of stem cells collected and delayed neutrophil engraftment respectively. A common standard protocol for hematopoietic stem and progenitor cells (HPSC) mobilization before ASCT in MM is currently not defined but the use of high dose cyclophosphamide (Cy) (3-4 gr/m2) seems associated with improved stem cell mobilization (SC) and collection with however an increase rates of severe neutropenia, infection and hospitalitazion. Moreover the administration of high dose of Cy, usually requires hospitalization to provide adequate hydration. The primary aim of this study is to assess the safety and efficacy of the mobilization therapy with low and high dose of Cy (2-3-4 g/m2) plus G-CSF in an outpatient setting. Materials and methods: From January 2022 to November 2022, 26 newly diagnosed multiple myeloma transplant eligible patients, 81% of them treated with daratumumab combination frontline, underwent mobilization with low (2 gr/m2; LD) and high dose (3-4 gr/m2; HD) Cy in outpatient setting. The LD-Cy was administered in one day while HD-Cy was split in two consecutive days (day +1 and +2). G-CSF (5 mcg/kg) was started at day +6. Use of plerixafor was permitted if circulating CD34+ cells were at least 5 uL at day +10. Eighty-five percent of patients received HD-Cy. Results: Chemotherapy was well tolerated. The most common adverse events (AEs) were hematological: grade 3-4 neutropenia (100%) and grade 3-4 thrombocytopenia (15%). The non hematological AEs of grade 3-4 were limited to one case of febrile neutropenia (G3) which required hospitalization. No treatment-related mortality was observed. 23% of patients reported non hematological mild AEs (G1-G2) including nausea, asthenia and constipation. The rate of AEs is independent of drug dosage. In our cohort no renal impairment neither worsening of renal function were observed. There was no statistically significant difference in median eGFR value before and after chemotherapy (at day +6). The median amount of SCs collected was 9.85×106/kg. The rate of mobilization failure (defined as failure to collect ≥2×106/kg) was 0%. One patient (3,8%) required use of Plerixafor. In 4 patients two consecutive apheresis sessions were required. Conclusion: Our results suggest that outpatient mobilization with low and high dose of cyclophosphamide is safe and may be considered for successful stem cell mobilization in MM transplant eligible patients treated with daratumumab frontline.

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