Primary mediastinal large B-cell lymphoma from the clinic to genomics: Insights for pathologists.

Primary mediastinal large B-cell lymphoma (PMBL) is a mature aggressive B-cell lymphoma that arises in the anterior mediastinum, likely originating from thymic B cells. Initially considered a subtype of diffuse large B-cell lymphoma, PMBL has since been established as a distinct clinicopathologic entity due to its unique clinical, morphologic, immunophenotypic and genetic characteristics. PMBL primarily affects young adults, especially women, and manifests as a bulky mediastinal mass that can invade adjacent structures, often causing respiratory symptoms. The genomic landscape of PMBL includes alterations in the JAK-STAT, NF-κB signaling pathways, and immune evasion mechanisms. This review explores the clinical presentation, pathogenesis and genetic landscape of PMBL, highlighting its morphologic and immunophenotypic characteristics and differences from related mediastinal lymphomas such as classic Hodgkin lymphoma and mediastinal grey zone lymphoma. We also discuss the implications of these findings on diagnosis, management and personalized treatment approaches.