Grey Zone Lymphoma: A Diagnostic and Therapeutic Challenge – A Case Report

Grey zone lymphoma (GZL) is a rare and aggressive B-cell lymphoma with features intermediate between primary mediastinal B-cell lymphoma (PMBL) and classical Hodgkin lymphoma (cHL). Its diagnostic complexity stems from significant morphological, immunophenotypic, and molecular overlaps with other lymphoma subtypes, often leading to misdiagnosis and suboptimal treatment. This case report describes a 34-year-old woman presenting with superior vena cava syndrome due to a large mediastinal mass, initially misdiagnosed as primary mediastinal B-cell lymphoma (PMBL) and later revised to GZL after comprehensive immunohistochemical analysis. Despite treatment with dose-adjusted EPOCH-R chemotherapy and salvage therapy, the disease progressed, highlighting the refractory nature of GZL. The introduction of pembrolizumab, an anti-PD-1 monoclonal antibody, marked a turning point, demonstrating significant clinical and metabolic response. This case underscores the diagnostic challenges of GZL, the limitations of conventional therapies, and the potential of immune checkpoint inhibitors in managing refractory disease. It emphasizes the need for a multidisciplinary approach, advanced diagnostic techniques, and personalized therapeutic strategies to improve outcomes in this complex and poorly defined lymphoma subtype. Further research is essential to refine treatment algorithms and identify predictive biomarkers for GZL.