Protein kinase c delta expression in primary central nervous system lymphomas

Primary central nervous system lymphoma (PCNSL) is a highly aggressive non-Hodgkin lymphoma confined to the central nervous system. Diffuse large B cell lymphoma (DLBCL) is the most common subtype, and it follows a much more aggressive course than its systemic counterpart. Differential diagnosis of PCNSL and systemic DLBCL depends on clinical staging, which is expensive and time consuming. Protein kinase C delta (PKCD) is a protein with proapopitotic properties and has a major role in negative selection of B cells in germinal centers, a regulatory function in B cell receptor (BCR) pathway and MHC II expression. Mutations identified in its gene are reported to be unique for PCNSL and not encountered in systemic DLBCL. Our aim is to evaluate immunohistochemical (IHC) expression and the mutation status of PKCD in PCNSLs and systemic DLBCLs in order to find out whether PKCD could be a novel marker that could be used in differential diagnosis of both entities. A total of 43 cases diagnosed with PCNSL, and 43 cases diagnosed with systemic DLBCL were included in the study. Immunohistochemistry for PKCD antibody and Sanger sequencing targeting exon 16 and exon 18 of PKCD gene were performed. Although immunoreactivity for PKCD was observed in all PCNSL and 95.3% of systemic DLBCL cases, strong and diffuse staining was found to be more frequent in PCNSL than systemic diffuse large B cell lymphomas (p < 0.001). However, mutations defined in literature were not encountered in our cohort. While clinical staging is still the primary way for differential diagnosis of PCNSL and systemic DLBCL, the diffuse and strong PKCD expression can be used as a supportive feature for PCNSL diagnosis