Mediastinal grey zone lymphoma, B cell lymphomas with intermediate features between classical Hodgkin lymphoma and primary mediastinal B cell lymphoma, are not well described in the literature. Investigators report the clinical characteristics and outcomes of a large retrospective series of 99 cases centrally reviewed by a panel of hematopathologists, with a consensus established for the diagnosis.

Inclusion Criteria:

• cases with an intermediate morphology and phenotype between CHL and PMBCL were included after central pathological review

Exclusion Criteria:

• Cases of CHL with partial CD20 expression or low expression in tumoral cells were excluded and considered as CD20-positive CHL
• Exclusion of sequential form patients (with a diagnostic biopsy of PMBCL and a relapse biopsy of CHL or vise-versa) as they represent a biases for statistical analysis.

We retrospectively identified cases treated in French, Belgium and Portuguese LYSA centers suspected to be MGZL using local pathological records, records from LYSA centers and the LYMPHOPATH network, which aims to review all newly diagnosed lymphoma cases in France (14). All the FFPE blocks and immunohistochemistry (IHC) slides (obtained prior any treatment) were centralized in the LYSA-Pathology (LYSA-P) department located in Henri Mondor hospital in Paris to perform a central review by a panel of hematopathologists. Two hundred and four cases were reviewed by the panel of LYSA hematopathologists.