In the WHO lymphoma classification, primary mediastinal (thymic) large B-cell lymphoma (PIVIVBL) 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 esere analyzed in the setting of 15 bioptically verified PIVIVBL 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 monocytoidlike cytoplasm. The described morphologic varianta of PIVIVBL might be related to the known genotypic variability of DLBCL, although monotypic c-Ig egpression 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, fit is recommended to prefer a diagnosis of DLBCL and to include the tumor finto a clinically defined subtype of PIVIVBL only in cases with well defined and typical clinical presentation and progression of the disease.

        Key words: diffuse large B-cell lymphoma - primary mediastinal large cell lymphoma - thymic origin - morphological heterogeneity.