[Primary mediastinal (thymus) large B-cell lymphoma: clinically defined type of tumors and morphologic variants]

In the WHO lymphoma classification, primary mediastinal (thymic) large B-cell lymphoma (PMVBL) is defined as a subtype of diffuse large B-cell lymphoma (DLBCL) showing typical clinical manifestation. The patterns related to variability of tumor cell morphology were analyzed in the setting of 15 bioptically verified PMVBL cases. In the majority of the cases (n = 12), the tumor showed pleomorphic blastic morphology with individual cell patterns resembling those of polymorphic centroblastoma of the Kiel classification. In addition, some of the cases had clear-cell and/or lacunar appearance (5/12), while distinctive anaplastic appearance was rare (1/12). Other cases (n = 3) showed a monotonous morphology of uniform smaller-sized blasts with monocytoid-like cytoplasm. The described morphologic variants of PMVBL might be related to the known genotypic variability of DLBCL, although monotypic c-Ig expression verified in some of the cases would support post-follicular stage of the tumor cell development. In the absence of clinical data and within the described morphologic variability, it is recommended to prefer a diagnosis of DLBCL and to include the tumor into a clinically defined subtype of PMVBL only in cases with well defined and typical clinical presentation and progression of the disease.