192 - Impact of Plerixafor Use at Different Peripheral Blood CD34+ Cell Thresholds on Autologous Stem Cell Collection in Patients with Multiple Myeloma

Abstract

Background: Since the introduction of plerixafor, uniform application in mobilization protocols has not been realized. Widespread use of plerixafor is limited by its price. Some institutions have adopted a conservative approach, reserving plerixafor for second mobilization attempts or predicted difficult mobilizations. Our institutional procedure has shifted from using a relatively stringent peripheral blood CD34 threshold to a more generous threshold for plerixafor administration. We report our experience with a risk-adapted strategy for plerixafor use at different pCD34 thresholds. Methods: We retrospectively evaluated patients with multiple myeloma and amyloidosis undergoing autologous stem cell collection with G-CSF mobilization from 1/2012-12/2016. Our algorithm for triggering plerixafor administration has evolved from a pCD34 count of <15/µL to <20/µL to <40/µL. Patients received G-CSF 10 mcg/kg daily for 4 days. On day 4, patients received plerixafor if the pCD34 was below the threshold and was continued until collection was completed. Plerixafor use, days of collection, collection yield, mobilization failure rates, and mobilization costs were calculated. Target collection yield is >4 × 106 CD34+ cells/kg, and an optimal mobilization would allow for two transplants. Results: We identified 348 mobilization attempts. Median age was 59.9 years (range, 28-74) and 60% were male patients. Most patients were in CR (n = 94), VGPR (n = 107), or PR (n = 98). On average, patients received 1.9 prior lines of systemic therapy. Plerixafor use increased from 80% in the <15/µL group to 91% in the <40/µL group, while average number of doses increased from 1.32 to 1.74 per mobilization. The average apheresis days decreased from 2.15 days for the <15/µL group to 1.89 days for the <40/µL group. For patients in the <15/µL and <20/µL groups, 23% completed collection in 1 day, and 65-70% completed within 2 days. For patients in the <40/µL group, 39% completed collection in 1 day and 77% completed within 2 days. A collection yield > 4 × 106 CD34+ cells/kg was reached in 91% of cases in the <15/µL group and 94% in the <40/µL group. More patients (51% vs 41%) collected >8 × 106CD34+ cells/kg in the <40/µL group than <15/µL group and reached that goal within 2 days (49% vs 32%). Mobilization failure rates were <5% across all thresholds. Mobilization costs were comparable. Conclusion: We demonstrate that a liberal strategy for plerixafor administration correlates with fewer apheresis days while having similar mobilization costs. There were 26 fewer days of collection per 100 mobilization attempts with a pCD34 threshold of 40/µL compared to 15/µL at our institution. More patients completed collection in one day, and more reached an optimal collection yield.