A Study of PD ‐L1 Expression in Intravascular Large B‐cell Lymphoma: Correlation with Clinical and Pathologic Features

: Intravascular large B cell lymphoma (IVLBCL) is a rare, aggressive, extranodal large B cell lymphoma characterised by growth of tumour cells within the lumen of vessels, particularly capillaries. Programmed cell death ligand 1 (PD-L1) is a cell surface glycoprotein that interacts with programmed death 1 (PD-1) on the T cell surface, leading to modulation of the immune response. PD-L1 is a targetable immune check-point molecule that is expressed on neoplastic cells in various cancers, including a subset of lymphomas. We correlated the expression of PD-L1 with clinical and pathological findings in this rare disease. Eleven cases of IVLBCL were identified in the archives of Laboratory of Pathology at the National Cancer Institute, NIH. A panel of immunostains (CD20, CD3, CD5, PD-L1) was performed. The cases were classified as the classic form or the variant associated with haemophagocytic syndrome (HPS) based on published 2017 WHO criteria. Three cases (27.3%) were HPS variant and eight cases (72.7%) were the classic form. Five (45.5%) of 11 cases were CD5-positive; two of three (66%) were HPS variants and three of eight (37.5%) were classic form. Overall, four of nine evaluable cases (44.4%) were positive for PD-L1, three of which were classic. Only one CD5-positive case was PD-L1-positive, a classic variant. In summary, a subset of IVLBCL express PD-L1. Although limited, these data suggest that PD-L1 is expressed in both the so-called classic form as well as the HPS variant. PD-L1 is expressed irrespective of CD5 expression. Finally, detection of PD-L1 expression in a subset of IVLBCL lymphoma cases may identify patients who might benefit from targeted immunotherapy.