Abstract 473: Higher levels of genomic complexity correlates with an advanced plasma cell differentiation status in newly diagnosed multiple myeloma patients

Introduction: plasticity is a hallmark of Multiple Myeloma (MM) clone(s), where both quiescent MM cells, acting as tumor-initiating cells, and proliferative MM cells, able to invade and disseminate, might co-exist. Aim of the study is to stratify patients (pts) according to both the level of chromosomal instability (CIN) and their plasma cells (PCs) differentiation stages, and to evaluate the impact of this stratification on the disease outcome. Patients & Methods: 145 newly diagnosed MM pts were included in the study. Whole-genome copy number alterations (CNAs) were analysed by SNP array both in the CD138+PCs and CD19+B-cells. In each pts, both the CD138+/CD38high PCs and CD19+B-cells compartments were characterized by 6-color multi-parameter flow cytometry analysis, combining CD138-PE, CD38-PE-Cy7, CD20-APC, CD19-APC-Cy7, CD27-FITC, CD45-FITC, CD28-APC, CD44-FITC, CD54-APC, CD81-PerCP-Cy5.5, CD56-APC. Results: According to the CD138+ PCs’ CIN, as described both by the total amount of CNAs and by the portion of genome changed (GC), three major pts subgroups were identified: the most representative, including 21/64 pts, was characterized by a higher CIN (median CNAs: 550 %GC ≥ 25) as compared to the others (intermediate and low CIN, median CNAs: 220 10≤ GC%≥25). Hyperdyploidy, but also high-risk features [i.e. 17p del (TP53)] mainly characterized CD138+ PCs with high CIN. On the contrary, in the same pts, the CD19+B-cells display a quite simple karyotype with very few microalterations (>50kb), mostly involved in the signal transduction pathway (loss on KRAS, chr12p12.1 and on SIRPB1, chr20p13). According to the the co-expression of CD19/CD81, describing the MM clone(s) differentiation status, PCs with a high level of CIN resulted more mature CD19-/CD81-. Both the high expression of CD28 and CD44 and the reduced expression of CD20, CD27 and CD45 confirmed the advanced differentiation status. Finally, although baseline clinical features of pts with more mature, genomically instable PCs, are associated to bad prognosis (e.g. PET lesions, k/l ratio, ISS III, β2-microglobulin; p Conclusion: High level of genomic complexity correlates with advanced PCs differentiation stages, and this is lastly associated with a prevalence of poor prognosis features. Both CIN and phenotypic pliancy represent important, yet poorly defined, mechanisms by which MM clone(s) accelerate their own evolution and survival. Acknowledgements: AIRC, AIL, HARMONY, Berlucchi Citation Format: Marina Martello, Rosalinda Termini, Enrica Borsi, Vincenza Solli, Andrea Poletti, Lucia Pantani, Serena Rocchi, Katia Mancuso, Elena Zamagni, Paola Tacchetti, Mario Arpinati, Gabriella Chirumbolo, Nicoletta Testoni, Giulia Marzocchi, Giovanni Martinelli, Michele Cavo, Carolina Terragna. Higher levels of genomic complexity correlates with an advanced plasma cell differentiation status in newly diagnosed multiple myeloma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 473.