Patterns of Change in Multiple Myeloma (MM) Clone Size with Autologous Hematopoietic Stem Cell Transplantation (ASCT) Assessed By Next Generation Sequencing (NGS) in Patients (pts) Receiving Modern Therapy

Background Measurable residual disease (MRD) is a quantitative, dynamic prognostic marker of progression free and overall survival in MM. With modern triplet and quadruplet induction strategies deep responses are the norm and the incremental effect of ASCT impact may vary substantially among pts and be influenced by disease and treatment features. However, the accurate characterization of the impact of ASCT is diluted by measuring a disease surrogate (paraprotein) instead of clone size. We examine the quantitative impact of ASCT on MM clone size by serial NGS testing before and after ASCT and evaluate disease and induction treatment features that modulate this impact. Methods We included pts with newly diagnosed MM from five US centers, who received modern triplet and quadruplet induction followed by single melphalan ASCT between 3/2018 and 5/2023 with MRD testing (ClonoSEQ®) pre and post ASCT. ClonoSEQ® platform utilizes NGS to quantify unique immunoglobulin genes rearrangements associated with MM clone, therefore directly capturing clone size. We excluded pts with clone size 1log 10 reduction in MRD burden with ASCT. The median log reduction in MRD burden was 1.15 (IQR 0.65-1.75). For pts with 0, 1 and 2+ HRCA, 47% (34/72), 68% (34/50), 74% (17/23) had a >1 log 10 reduction in clone size and the median reduction was 0.96 log 10 (IQR 0.47-1.66), 1.24 log 10 (IQR 0.89-1.91) and 1.5 log 10 (IQR 0.89-2.20), respectively (Figure). Among pts without HRCA, those with hyperdiploid MM had a trend towards less frequent ≥1 log 10 clone size reduction with ASCT (38% vs. 57%,