PF560 A MATURATION INDEX DEFINES NEWLY DIAGNOSED MULTIPLE MYELOMA PATIENTS WITH ADVANCED IMMUNOPHENOTYPIC AND MOLECULAR DIFFERENTIATION PROFILES ASSOCIATED WITH POOR PROGNOSIS
Authors: M. Martello, R. Termini, E. Borsi, V. Solli, A. Poletti, L. Cifarelli, L. Agboyi, L. Pantani, S. Rocchi, K. Mancuso, E. Zamagni, P. Tacchetti, M. Arpinati, G. Chirumbolo, A. Orlando, G. Marzocchi, N. Testoni, G. Martinelli, M. Cavo, C. Terragna
Journal: HemaSphere (2019)

Background: The differentiation status plasticity of Multiple Myeloma (MM) plasma cells (PC) is an adaptive strategy that might confer a specific fitness to tumour cells, enabling their interaction to an evolving microenvironment. Therefore, MM clones are not constantly “fit”, and the immunophenotypic profile of the fittest MM PCs might be the expression of specific genetic and genomic programs, emerging under therapeutic pressure and promoting tumour development. However, the genomic background that supports any diverse plasma cell differentiation phenotypes has not yet been inferred. Aims: To correlate the genetic and genomic background with the immunophenotypic profile of MM clones at diagnosis, in order to stratify patients (pts) according to a Maturation Index , and ultimately to evaluate the impact of this stratification on the disease outcome. Methods: 114 newly diagnosed MM pts were included in the study . For each pts, both the neoplastic PCs and CD19+ B cells compartments were characterized by 6‐color multi‐parameter flow cytometry analysis, combining CD138‐PE, CD38‐PE‐Cy7, CD56‐APC‐Cy7, CD20‐APC, CD19‐FITC, CD27‐APC, CD45‐PerCp, CD28‐APC, CD117‐FITC, CD28‐APC, CD81‐APC, IgK‐APC and IgL‐FITC. Both whole‐genome copy number alterations (CNAs) and a 25‐genes targeted mutational panel were assessed in CD138+ PCs. A custom ddPCR assay was employed to evaluate the self‐renewal status of PCs. Results: In order to define a Maturation Index , pts were evaluated for: a) differential expression of CD19/CD81 markers; b) level of chromosomal instability (CIN); c) self‐renewal status. According to the CD19 and CD81 markers co‐expression, we were able to stratify pts in 3 different subgroups, recapitulating a progressive PC maturation process: the most immature, which included pts with PCs CD19+/CD81+ (20/114 = 17%); an intermediate CD19‐/CD81+ phenotype subgroup (40/114 = 35%); and the CD19‐/CD81‐ PC subgroup (54/114 = 48%), whose clone was mainly composed by most mature plasma cells. CIN was defined according to both the total CNAs count and the portion of genome changed (GC). Pts with an advanced differentiation status (CD19‐/CD81‐) were more frequently associated to a high CIN (medium tot. CNAs = 550, % GC ≥ 25%), including a higher prevalence of high‐risk features. Indeed, 1p deletion ( FAF1 ), 16q deletion ( WWOX , FANCA ) and 17p deletion ( TP53 ) were the most recurrent abnormalities. Genomic instability was also confirmed by a higher incidence of clonal pathogenic mutations in critical genes (e.g. NRAS , KRAS , TP53 ). Interestingly, the application of a 10 Hh‐genes signature, resuming the Hedgehog pathway, demonstrated that PCs with more advanced differentiation status displayed a substantial overexpression of all the genes, indicating a more proliferative, aggressive and, possibly, persistent phenotype. Finally, the presence of a more mature PCs characterized pts carrying baseline clinical features associated to bad prognosis (e.g. n. PET lesions, k/l ratio, ISS III, β2‐microglobulin; p &lt; .05). In addition, these pts tended to obtain high quality response rates (≥VGPR) to PI induction therapy. Summary/Conclusion: An iMMature index defined pts with an advanced differentiation status both at immunophenotypic as well as at molecular level, and this is lastly associated with a prevalence of bad prognosis features. Chromosomal instability, together with cellular phenotypic plasticity, represents an important, yet poorly defined, mechanism by which MM clones accelerate their own evolution and survival. Acknowledgements: AIRC IG2014, Fondazione Berlucchi.