Primary Mediastinal Large B-cell Lymphoma: Diagnostic Challenges and Recent Advances

Abstract

Primary mediastinal (thymic) large B-cell lymphoma (PMBL) is a subtype of uncommon aggressive large B-cell lymphomas primarily occurring in mediastinum although rare cases with non-thymic type of PMBL have been reported. Typical PMBL has characteristic clinical, morphological, and immunophenotypic features which the pathologists use as diagnostic paradigm in routine practice. However, the diagnosis can be occasionally challenging due to the overlapping clinicopathologic features with other lymphomas, among which are nodular sclerosis classic Hodgkin lymphoma, systemic diffuse large B-cell lymphoma (DLBCL) involving mediastinum, and B-cell lymphoma, unclassifiable, with features intermediate between DLBCL and classic Hodgkin lymphoma (gray zone lymphoma). Recent depictions of the characteristic genetic/ molecular aberrations and unique gene expression profiling in PMBL have provided a robust tool to significantly improve the diagnostic accuracy. In addition, the progresses in understanding the pathogenesis of PMBL have paved the way discovering novel therapeutic agents for patients with refractory/relapsed disease.