Primary Bone Lymphoma Exhibits a Favorable Prognosis and Distinct Gene Expression Signatures Resembling Diffuse Large B-Cell Lymphoma Derived From Centrocytes in the Germinal Center.

Primary bone (PB) diffuse large B-cell lymphoma (DLBCL) is rare and has a favorable prognosis, but the underlying biological mechanisms remain unknown. In this study we analyzed the clinicopathologic features of 160 patients with PB-DLBCL in comparison with 499 nonosseous DLBCL. Compared with patients with nonosseous DLBCL and secondary involvement of bone by DLBCL, PB-DLBCL patients less frequently had elderly age, B-symptoms, elevated serum lactate dehydrogenase levels, and high International Prognostic Index at diagnosis, more frequently had germinal center (GC) subtype (approximately 90%) and complete remission, and had significantly better survival. The 5-year progression-free and overall survival rates of PB-DLBCL patients were 80% and 93%, respectively, superior to both GC B-cell-like (GCB) and activated B cell-like subtypes of DLBCL. Further stratifying nonosseous DLBCL cell-of-origin subtypes by clinical factors showed that PB-DLBCL had similar survival rates as the centrocyte-origin (CC) subtype of DLBCL-GCB classified by the B-cell-associated gene signature algorithm. To better understand the favorable outcome of PB-DLBCL patients, gene expression profiling and microRNA profiling were performed in a small subset of PB-DLBCL. The gene expression profiles of PB-DLBCL resembled those of nonosseous DLBCL-GCB-CC, but were distinct from other DLBCL cell-of-origin especially the centroblast-origin (CB) subtype. Compared with DLBCL-GCB-CB, PB-DLBCL and DLBCL-GCB-CC also had much higher levels of miR-125a-3p, miR-34-3p, and miR-155-5p, and significantly lower levels of miR-17-5p and miR-17-3p. These results demonstrated that PB-DLBCL is clinically distinct, and the cell-of-origin of PB-DLBCL stems from centrocytes in the GC, that are biologically attributed for the favorable prognosis of PB-DLBCL.