Peripheral Blood Hematopoietic Progenitor Cell (HPC) Counts At Autologous Stem Cell Collection (ASCC) Are Associated with Prognosis in Multiple Myeloma
Authors: Choi Yoon Ji , Yoon Dok Hyun , Jo Jungmin , Lee Kyoungmin , Kang Eun Hee , Kim Shin , Jang Seongsoo , Park Chan Jeoung , Chi Hyun Sook , Suh Cheolwon 
Published: October 2019

Abstract
Abstract 4412

Background
High-dose chemotherapy followed by autologous stem cell transplantation (HDC-ASCT) has been adopted as the first-line treatment for young and/or fit patients with multiple myeloma, providing higher remission rates. However, only few factors have been identified affecting the outcome in such patients. One previous retrospective study suggest that high levels of mobilized peripheral CD34+ cells are associated with favorable outcome in myeloma patients undergoing HDC-ASCT. However, prognostic significance of hematopoietic progenitor cell (HPC) count (Suh C, Transfusion 2004), an estimate of immature cells used for timing stem cell harvest instead of CD34+ cell count, has not been investigated yet.

Methods
We measured peripheral HPC counts at the day 1 of autologous stem cell collection (ASCC) by Sysmex SE9000 in 112 myeloma patients at the Asan Medical Center between May 2000 and May 2012. Patients were divided into two groups (super vs normal mobilizers) with a cutoff of 50 HPC count per μL.

Results
Among 112 patients, 34 had more than 50 HPCs per μL (super mobilizers) and 76 had less than 50 HPCs per μL (normal mobilizers). The two groups showed no differences with regards to age, sex, subtype, light chain, ISS stage at diagnosis, performance, cytogenetics, BM plasma cells, the regimen used for induction chemotherapy and response to induction chemotherapy. However, more patients of super mobilisers received tandem ASCT comparing to normal mobilizers (35.3% vs 14.3%; p=0.052). In addition, all super mobilizers received chemotherapy combined with growth factor as mobilization, 15.6% of normal mobilizers received growth factor only (p=0.017). The mean number of HPCs in the super mobilizer group was 167.3 ± 25.7 per μL, and 16.5 ± 1.5 per μL in the normal mobilizer group (p<0.001). The total number of CD34+ cells collected at apheresis was higher in the super mobilizer group (23.9 ± 2.5 × 106 per kg vs 17.5 ± 1.34×106 per kg; p=0.029) and the super mobilizer group tended to receive more CD34+ cells at transplantation (13.6 ± 1.5 × 106 per kg vs. 10.5 ± 0.9 × 106 per kg; p=0.063). However, time to engraftment was not different between two groups.
After a median follow-up of 81.6 months, progression free survival (PFS) did not differ between the arms (18.87 months vs 19.47 months; p=0.937). However, the super mobilizer group showed a relatively longer overall survival (OS), with a median OS of 77.9 months compared with 48.9 months in the normal mobilizer group (p=0.099). In multivariate analysis, good performance (p=0.046) and response to induction treatment (p=0.009) were associated with prolonged OS. And the level of peripheral HPCs also revealed to be an independent prognostic factor for OS (HR=0.518, 95% CI: 0.285–0.940; p=0.031).

Conclusion
Our results suggest that high levels of peripheral HPCs at the day 1 of apheresis might be an independent prognostic factor for OS in myeloma patients undergoing HDC-ASCT, which warrants further investigation

Disclosures:
No relevant conflicts of interest to declare.