Superior survival in diffuse large B cell lymphoma of the bone with immune rich tumor microenvironment

With tumor genomic and gene-expression profiling (GEP), this study investigated the immune-molecular signatures of a unique cohort of diffuse large B-cell lymphoma of the bone (bone-DLBCL), including primary bone (PB-DLBCL, n = 52) and polyostotic-DLBCL (n = 20), in comparison to nodal DLBCLs with germinal center B-cell (GCB) phenotype (nodal-DLBCL-GCB, n = 34). PB-DLBCL and polyostotic-DLBCL shared similar genomic profiles and transcriptomic signatures, justifying their collective analysis as bone-DLBCL. Differential incidences of EZH2, HIST1H1E, and MYC aberrations (p < 0.05) confirmed the distinct oncogenic evolution between bone-DLBCL and nodal-DLBCL-GCB. Differentially expressed genes were identified between bone-DLBCL and nodal-DLBCL-GCB (p < 0.001), substantiated by distinct gene-set enrichment analysis (GSEA). In contrast to a more 'depleted' phenotype for nodal-DLBCL-GCB, bone-DLBCL primarily exhibited an 'intermediate/rich' tumor microenvironment (TME) signature (p = 0.001), as determined by a previously published gene set. Unsupervised clustering defined two distinct groups that aligned with previously reported immune-enriched TME clusters: an 'immune-rich' cluster largely consisting of bone-DLBCLs (75%, p = 0.002) with superior survival (p = 0.030), and a poor-prognostic 'immune-low' cluster, including mostly nodal-DLBCL-GCB (61%). Single-sample (ss)GSEA showed higher scores for regulatory T cells, immunosuppressive/prolymphoma cytokines, and vascular endothelial cells in immune-rich samples (p < 0.001). Additionally, CIBERSORTx revealed a higher abundance of regulatory T cells and activated mast cells in the immune-rich cluster (p < 0.001). These findings were confirmed at protein level, where CD3 and FOXP3 immunochemistry showed significant overlap with the gene-expression data (p < 0.001). Conclusively, PB-DLBCL and polyostotic-DLBCL share immune-molecular TME characteristics, supporting their classification as a unified bone-DLBCL entity. The distinct immune-rich TME profile of bone-DLBCL associated with superior survival potentially shapes emerging immunomodulatory strategies.