Abstract 1758: A more mature immunophenotypic makeup of multiple myeloma clone(s) at diagnosis correlates with a higher genomic instability
Authors: Martello Marina , Termini Rosalinda , Santacroce Barbara , Borsi Enrica , Solli Vincenza , Pantani Lucia , Zamagni Elena , Tacchetti Paola , Ulbar Francesca , Chirumbolo Gabriella , Arpinati Mario , Martinelli Giovanni , Cavo Michele , Terragna Carolina 
Published: July 2017

Intro The sequence of events underlying the process of Multiple Myeloma (MM) plasma cells (PC) differentiation have not yet fully elucidated, even if recent findings suggest that different cell subpopulations, with distinct phenotype, compose the MM clone(s), whose plasticity has emerged as a typical feature.

Aim To evaluate the phenotypic plasticity and genomic background of MM clone(s) at diagnosis in order to stratify patients (pts) according to the PC differentiation stages and possibly correlate with disease outcome.

P&M Phenotypic characterization of both CD138+/CD38+ and CD19+ populations was carried out on 44 newly diagnosed MM. Fresh BM samples was analysed by 6color multiparametric flow citometry analysis, combining CD138PE, CD38-PE-Cy7, CD20-APC, CD19-APC-Cy7, CD27-FITC, CD45-FITC, CD28-APC, CD44-FITC, CD54-APC, CD81-PerCP-Cy5.5, CD56-APC and SHH-PE, as a functional marker of Hedgehog pathway activation (Miltenyi Biotech). Cytoscan HD array were carried out in order to detect genomic copy number alterations (CNAs).

Results According to the CD19 and CD81 markers co-expression, pts were stratified in 3 subgroups, recapitulating a progressive PC maturation process: the most immature one, including pts with CD19+/CD81+ PC (11/44 = 25%); the intermediate CD19-/CD81+ phenotype one (19/44 = 43%), and the CD19-/CD81- PC one, whose clone was mainly composed by most mature PCs.

The two extreme subgroups were characterized by a differential expression of maturation markers: the more mature PCs displayed a higher expression of CD28 and CD44, which usually characterized advanced disease stages, as well as a reduced expression of CD20, CD27 and CD45, commonly associated to preceding PC differentiation stages (p&lt;.05). Any differential expression of SHH pathway’s ligand was observed. On the contrary, a higher Hedgehog pathway activation was detected in the immature CD19+ compartment of pts with immature plasma cells (median SHH expression CD19+/CD81+ vs. CD19-/CD81-: 98,1% vs. 11,3%; p&lt;.05), which probably highlighted a less quiescent immature reservoir pool.

The CNAs analysis showed that mature PCs were characterized by a higher genomic instability, as compared to the more immature ones (total CNA: 306.9 vs. 171.5, p 0.08; genome changed: 36.96 vs. 13.55, p 0.01), including several alterations commonly associated to worse prognosis (e.g. del17p).

Finally, a higher frequency of baseline clinical characteristics associated to bad prognosis was observed in the more mature, as compared to the more immature subgroups of pts (e.g. n. PET lesions, k/l ratio; p&lt;.05).

Conclusion MM clone(s) is a mixture of different cell populations endowed with an inner phenotypic plasticity. Various PC differentiation stages were appreciable already at diagnosis and genomic features associated to bad prognosis characterize pts carrying more mature clones.

Acknowledgements: AIRC, Berlucchi, Prog. Bolondi, FUV

Citation Format: Marina Martello, Rosalinda Termini, Barbara Santacroce, Enrica Borsi, Vincenza Solli, Lucia Pantani, Elena Zamagni, Paola Tacchetti, Francesca Ulbar, Gabriella Chirumbolo, Mario Arpinati, Giovanni Martinelli, Michele Cavo, Carolina Terragna. A more mature immunophenotypic makeup of multiple myeloma clone(s) at diagnosis correlates with a higher genomic instability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1758. doi:10.1158/1538-7445.AM2017-1758