P-043: Comparison of MRD detection of autografts in multiple myeloma between novel high-sensitivity EuroFlow-NGF and NGS

Abstract

<h3>Background</h3> Autologous stem cell transplantation (ASCT) is still a gold standard treatment in multiple myeloma (MM). So far, we have reported the prognostic value of minimal residual disease (MRD) detection in autografts at ASCT setting using EuroFlow next-generation flow (NGF) and next-generation sequencing (NGS) (Takamatsu et al, ASH 2018). The main problem of EuroFlow-NGF is its lower sensitivity (2×10^-6) compared with that of NGS (<1×10^-6). <h3>Methods</h3> The study enrolled 9 newly-diagnosed MM patients whose frozen autografts' cells were preserved. The median age at ASCT was 52 (range 47-61) years and included 4 males and 5 females at ISS I (n=2), II (n=6) and III (n=1). Of there, 4 patients harbored high-risk chromosomal abnormalities including t(4;14) (n=1), t(14;16) (n=1), del17p (n=1), and t(4;14) and del 17p (n=1). All patients received bortezomib-based chemotherapy for induction together with melphalan at 200 mg/m² for conditioning before ASCT. Two patients received consolidation therapy with carfilzomib-lenalidomide-dexamethasone (KRD) and all patients received lenalidomide maintenance until progressive disease. Frozen autografts (n=9) and primary myeloma cells (n=1) were thawed for MRD assessment by EuroFlow-NGF and NGS. The EuroFlow-NGF method was based on the previous report (Flores-Montero et al., Leukemia 2017). NGS-based MRD assessment was performed using Adaptive's standardized NGS-MRD Assay (Seattle, WA) (Ching et al., BMC Cancer 2020). The EuroFlow-NGF method was modified to increase the sensitivity of MRD by capturing cells up to 5×10⁷. <h3>Results</h3> Because frozen autografts were used in this study, we performed the sensitivity test using the dilution of frozen/thawed primary MM cells in an autograft by EuroFlow-NGF. The sensitivity test revealed a strong correlation between 1×10^-7 and 1×10^-4 of MRD level (r=0.9996, p<0.0001). Next, MRD in autografts (n=9) was evaluated using EuroFlow-NGF and NGS. The sensitivity of NGS was 6×10^-7–8.7×10^-5 (median, 8×10^-7) using 2–4 mL of autografts; the sensitivity of EuroFlow-NGF was 4×10^- ⁷–8×10^-7 (median, 5×10^-7) using up to 20 mL of autografts. MRD levels in autografts using EuroFlow-NGF and NGS correlated with one another (r = 0.9964, P < 0.0001). There was no discrepancy of MRD levels between both methods: negative (n=2), 10^-6-10^-5 (n=4), 10^-5-10^-4 (n=2), 10-4 < (n=1). All high-risk chromosomal abnormality cases (n=4) achieved MRD level <10^-5. The response on day 100-300 post-ASCT included 6 sCR, 2 CR and 1 VGPR before consolidation/maintenance therapy and all patients achieved sCR at two years post-ASCT and maintained it at three years post-ASCT during lenalidomide maintenance. No progression was observed. <h3>Conclusions</h3> This modified EuroFlow-NGF method can assess MRD of frozen/thawed autografts and its sensitivity can be increased up to 4×10^-7 that is comparable to NGS.