Immunohistochemical Assessment of the Diagnostic Utility of PD-L1 (Clone SP142) for Methotrexate-Associated Lymphoproliferative Disorders with an Emphasis of Neoplastic PD-L1 (Clone SP142)-Positive Classic Hodgkin Lymphoma Type

Objectives: We describe results of programmed death ligand 1 (PD-L1) immunohistochemical assessment in methotrexate (MTX)-associated lymphoproliferative disorders (LPDs) and highlight the characteristics of classic Hodgkin lymphoma (CHL) type MTX-LPD. Methods: Fifty cases of MTX-LPD, including CHL type (n = 9), diffuse large B-cell lymphoma type (n = 15), and polymorphic B-cell LPD (n = 21), were investigated. Results: Staining with anti-PD-L1 clone SP142 was exclusively found in CHL type (89%) but not in the others. Cases of CHL type MTX-LPD involved nodal disease and were associated with Epstein-Barr virus. They were histopathologically characterized by a vaguely nodular pattern, predominance of mononuclear cells, and strong expression of at least one pan-B-cell marker. Their clinical course was variable, with spontaneous regression in 5 patients, relapse in 2, and a fatal course in 1. Conclusions: The PD-L1 (clone SP142) workup aids the diagnostic approach to patients with MTX-LPD. CHL type MTX-LPD appears to represent a unique morphologic variant of CHL.