Background: The 2022 World Health Organization (WHO) classification redefines the concept of gray zone lymphoma (GZL), restricting it in practice to cases of mediastinal/thymic origin (mediastinal gray zone lymphoma, MGZL) with overlapping features between primary mediastinal B-cell lymphoma (PMBCL) and classical Hodgkin lymphoma (CHL). Cases with histological characteristics of GZL but occurring without mediastinal involvement are better classified as diffuse large B-cell lymphoma, not otherwise specified (DLBCL NOS), with few exceptions.
Procedure: We collected clinical and pathological data about all Italian pediatric patients diagnosed with GZL over a 20-year period.
Results: We identified only four cases of bona fide MGZL. All patients were adolescent and presented with a mediastinal disease, always associated with other nodal involvement. B symptoms and increased levels of both erythrocyte sedimentation rate (ESR) and lactate dehydrogenase (LDH) were observed. Only two patients achieved a first complete remission, suggesting a more aggressive clinical behavior than either PMBCL or CHL.
Conclusion: Prospective studies evaluating prognostic factors and establishing the most effective first-line therapy for MGZL are highly needed.
Keywords: WHO classification; gray zone lymphoma; mediastinum; pediatrics.
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