Primary sinonasal large B cell lymphoma is as histopathologically heterogeneous as systemic large B cell lymphoma but may show subtype-specific tropism for specific sinonasal anatomic sites.

Large B cell lymphomas (LBCL) are a heterogeneous group of diseases with variable presentations and prognoses. Rarely, LBCLs arise in the sinonasal tract and are distinct from extranodal NK/T-cell lymphoma which is more typical in this anatomic location. We hypothesized that large B cell lymphoma primary to the sinonasal tract (snLBCL) would be heterogeneous and include high-grade B cell lymphomas (HGBCL) described in the revised 4^th edition WHO classification of lymphomas. We retrospectively evaluated cases of snLBCL at our center, and performed additional immunohistochemical and in situ hybridization studies where needed for modern WHO classification. Our cohort consisted of 25 cases, 15 males and 10 female patients, aged 14 to 87 years, with predominantly nasopharyngeal disease (n = 11), Ann Arbor stage IIE (n = 15), and immunocompetence (n = 24). According to revised 2016 WHO criteria, 20 of the 25 cases were DLBCL-NOS (80%, two-thirds germinal center phenotype), 3 were HGBCL-NOS (8%, one with MYC rearrangement without BCL2 rearrangement), and 2 were EBV-LBCL (8%). Among DLBCL-NOS, those arising in the nasopharynx all showed a germinal center B cell (GCB) phenotype, whereas both evaluable maxillary sinus tumors showed non-GCB characteristics (p = 0.02). These data show that large B cell lymphoma primary to the sinonasal tract is histopathologically heterogeneous as systemic large B cell lymphoma. The observation that GCB and non-GCB tumors differs in anatomic location suggests that microenvironmental factors in sinonasal anatomic sites may drive lymphoma characteristics. [ABSTRACT FROM AUTHOR]