Syncytial variant of classic Hodgkin lymphoma: Four cases diagnosed with the aid of CD274/programmed cell death ligand 1 immunohistochemistry.

Although several reports have highlighted neoplastic PD-L1 (nPD-L1) expression in classic Hodgkin lymphoma (CHL), some have addressed associations between its expression and detailed histopathologic features. Here we describe four cases of syncytial variant of CHL (SV-CHL), with and without Epstein-Barr virus (EBV) association, and highlight the diagnostic utility of PD-L1 (clone SP142) immunohistochemistry. The patients were a 61-year-old male, 45-year-old male, 85-year-old female, and 89-year-old female. All presented with cervical or axillary lymphadenopathy, which on biopsy had the established histopathologic features of SV-CHL with a biphasic pattern of cohesive sheets of large tumor cells and typically scattered distribution of Hodgkin and Reed-Stenberg (HRS) cells. These tumor cells showed identical immunophenotypic findings for CD15, CD30, Fascin, PAX5, OCT2, BOB1 and EBV harboring, regardless of location. The exception was absent or decreased expression of nPD-L1 from tumor cells in the confluent sheets, contrasting with HRS cell positivity in typical areas of CHL. These findings offer the first suggestion of possible downregulation of nPD-L1 expression in association with the histopathologic progression of CHL. The results may be relevant for recognizing 'confluent' sheets in the diagnostic workup for SV-CHL.