B-CELL RECEPTOR SIGNALING ACTIVITY IDENTIFIES PATIENTS WITH MANTLE CELL LYMPHOMA AT HIGHER RISK OF PROGRESSION

Mantle cell lymphoma (MCL) is an incurable B-cell malignancy characterized by high clinical variability, with some patients present- ing with indolent disease while others experiencing aggressive clin- ical course. There is a critical need to define parameters that identify patients at higher risk of progression and therapy resistance for guid- ing clinical decisions. B-cell receptor (BCR) signaling is crucial for MCL initiation and progression and is a target for therapy. We mea- sured the phosphorylation status of nine BCR signaling phosphopro- teins (SYK, LCK, BTK, PLCγ2, p38, ERK1/2, AKT, NF-κB p65, STAT5) using phospho-specific flow cytometry in peripheral blood mononuclear cells (PBMCs) from 30 MCL patients, in the basal con- dition and following BCR modulation with anti-IgM antibodies. Flow-cytometry data were subjected to unsupervised hierarchical cluster analysis (HCA) within the MCL samples. Progression free survival (PFS) and overall survival (OS) curves were estimated using the Kaplan-Meier method and compared using the log-rank test. Uni- variate and bivariate models for PFS and OS were generated using Cox proportional hazards regression. BCR modulation with anti-IgM induced activation of BCR signaling that was heterogenous among patients’ samples. Unsupervised HCA of BCR responsiveness to anti- IgM modulation within the MCL samples identified two main clus- ters showing differential responses to BCR stimulation. The cluster comprising samples with higher BCR signaling response (HR) was associated with shorter survival than cluster with lower BCR signal- ing response (LR) (median PFS: 15 versus 40 months, respectively, log-rank test P=0.042; median OS: 27 versus 52 months, respec- tively, log-rank test P=0.041; Figure 1). n conclusion, we identified BCR signaling properties that were associated with poor clinical outcome and resistance to ibrutinib, thus highlighting the prognostic and predictive significance of BCR ac- tivity in MCL and advancing our understanding of signaling hetero- geneity underlying clinical behavior of MCL. We thank Fondazione Italiana Linfomi (PGR Ed. 2019) for funding support.