Tetsuya Tsukamoto

Abstract CD5 expression is seen in 5%–10% of de novo diffuse large B‐cell lymphomas (DLBCLs). Primary large B‐cell lymphoma of the central nervous system (PCNS‐LBCL) also exhibits CD5 expression in a minority of cases, however, clinicopathological and molecular features remain largely unclarified. Here we present the clinical, molecular, and pathological features of 11 CD5‐positive (⁺) PCNS‐LBCL cases, occupying 6.7% of all 165 PCNS‐LBCLs diagnosed in our institutions. While CD5⁺ systemic DLBCL has been recognized as a distinctive subgroup showing an aggressive clinical course, no obvious differences were found between CD5⁺ and CD5‐negative subgroups among the present CNS patients clinically. MYD88 p.L265P and CD79B p.Y196 mutations were detected in eight (73%) and seven (64%) cases, respectively, supporting previous reports. Notably, the microenvironmental immune cells were universally PD‐L1/CD274‐positive, and the higher levels tended to present favorable overall survival, as already evidenced in the PCNS‐LBCL series. In contrast, neoplastic PD‐L1/CD274 expression was undetectable in all cases. Indeed, no structural variations or copy number alterations involving PD‐1 ligands were detected by targeted‐capture sequencing and fluorescence in situ hybridization. While further studies are warranted, we may have confirmed similarity between PCNS‐LBCLs and intravascular large B‐cell lymphomas from a molecular standpoint.