Utilization of Leftover Autologous Peripheral Blood Stem Cells (PBSCs) in Patients with Multiple Myeloma (MM)
Authors: Callander Natalie S , Longo Walter L. , Juckett Mark B. , Kenkre Vaishalee P. , Hematti Peiman , McMannes Janelle , Evans Rebecca K , Eckstein Linda A , Gage Blythe 
Published: November 2019

Abstract
Autologous PBSCT remains an integral part of therapy for MM patients (pts) but the sequencing and repeat applications of this intervention vary among transplant centers. Current NCCN guidelines (V 2.2014) and expert panels (e.g. IMWG Consensus Statement, Leukemia10: 1904) recommend collecting sufficient PBSCs for 2 transplants and indefinite storage. As MM survival continues to improve, the period between initial treatment and first or salvage PBSCT may span years. Many centers face issues of overflowing freezers, unreimbursed storage costs and referring providers opting for salvage treatment options other than PBSCT. Outside providers may also be unaware or forget that previously collected PBSCs are available for transplant or doubt the usefulness of the treatment. We therefore analyzed the fate of PBSCs collected for MM pts from 2005-2013 at our center.
METHODS: All MM pts who underwent any attempt at PBSCT collection between 2005 and 2013 (n=304) were included. UW Stem Cell lab provided storage records, medical records were reviewed to establish current clinical status, treating physicians and patients were also contacted.
RESULTS: 304 MM pts had PBSCs collected between 2005-2013. This accounted for 479 apheresis procedures, median 2/pt., range 1-4, with a median of 2 aliquots per procedure stored totaling 930 aliquots (median 2/pt.; range 1-10). Ultimately, 267 underwent PBSCT. Of those pts, 98 (32%) used all collected cells. Leftover cells remained for 206 pts (68%) during this 9 year time span. Of those, 37 pts (18% of those with leftover cells) have never undergone transplant (Table 1)
Table 1. Outcome of patients who have never used stored PBSCs (n=37) OUTCOME Number Percentage (n=37) Have not progressed from initial therapy 19 51% Pt refused transplant 6 14% Never offered ; died of MM 14% Collection Inadequate 2 5% Cells sent to other transplant site 2 5% Transplant pending 3 8% Not offered due to PD 1 3%
PD= progressive disease;
The remaining 169 pts had a least one PBSCT and had leftover aliquots (82%) (Table 2)
Table 2. Outcome of patients receiving one PBSCT with remaining cells OUTCOME Number Percentage Have not progressed from PBSCT 88 52% Died of PD; 2nd PBSCT never offered 23 14% Relapsed, alive, 2nd PBSCT not offered 17 10% Relapsed <6mo after 1st PBSCT; salvage transplant not offered 13 8% ( all pts died of PD) Pt refused 2nd PBSCT 12 7% (all pts died of PD) Died of non-MM causes 5 3%* Second PBSCT planned 5 3% Salvage allo offered instead 4 (3 Died of PD) 2% Too old for 2nd transplant 1 0.6% Died during 1st transplant 1 0.6%
*Secondary malignancy-4, accidental death-1
CONCLUSIONS: The collection and prolonged storage of PBSCs for patients with MM has become routine. We found that 12% of patients with stored PBSCs never used any cells collected, but the majority of these pts had not progressed. In addition, 30% of previously transplanted pts with stored cells either refused or were not referred back for second transplant consideration despite disease progression, with 44% dying of MM. Patients and providers should be educated regarding the availability of these products for first or salvage PBSCT and favorable outcomes that have been reported with these interventions, even in the era of novel agents. Transplant centers should consider periodic notification of MM providers and patients underscoring the availability of their stored cells for use.

Disclosures
No relevant conflicts of interest to declare.