Abstract 640: Genome sequencing of circulating multiple myeloma cells for minimally invasive molecular characterization of precursor disease pathology

Introduction: Multiple myeloma (MM) develops from indolent stages monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). Precursor conditions are incidentally diagnosed and require invasive bone marrow (BM) biopsies for complete characterization, highlighting the urgent need for improved early detection methods. Minimally invasive blood biopsies to measure circulating multiple myeloma cells (CMMCs) as markers of MM disease development are a promising solution to this unmet need. Here, we present our novel method CatchTheFISH, for whole genome sequencing (WGS) of CMMCs that enables genomic profiling and WGS based cytogenetic analyses from enriched liquid biopsy samples. Application of WGS in a cohort of 20 patients, revealed CMMCs were of tumor origin and able to faithfully match BM sequencing results and detect 100% of clinically reported events. Methods: Peripheral blood from 110 SMM patients from the PCROWD observational study (Dana-Farber Cancer Institute IRB #14-174) was collected and processed on CellSearch system (Menarini Silicon Biosystems), with enrichment and enumeration of CMMCs based on CD138+38+CD45-19- immunophenotype. In 20 patients, CMMCs and white blood cells were sorted for library construction, quantification and WGS on Illumina NovaSeq6000. Mutation analyses were performed with the cancer genome analysis pipelines of the Broad Institute. Results: CMMCs were detected in 84% of SMM patients enrolled in the study, with a median count of 13 CMMCs (range 0 to 43836). We first demonstrated the concordance of WGS results obtained from CMMCs with BM. In 100% of patients tested with paired BM and CMMCs (n = 8), we observed full agreement in structural event calling between our samples and clinical reports, including translocations and CNAs (trisomies, tetrasomy, monosomy 13 and 1q gain/amplification). Next, we showed WGS of CMMCs provided increased diagnostic yield compared to BM biopsy for the detection of structural events and MM-associated driver mutations. In 7 patients (88%) we detected additional aberrations not found by FISH. Unknown translocation events of IGH-MYC and t(14;20) were distinguished in two patients. Additionally, our method enabled detection of MM driver mutations. Three patients (38%) were found to harbor RAS mutations (KRAS and NRAS) in BM samples, which were also validated in matched CMMCs. Finally, we assessed a validation cohort of 12 SMM patients with CMMCs only. WGS detected c