Fibrin-associated large B-cell lymphoma arising within a hepatic cystic lesion: a case report.

Fibrin-associated large B-cell lymphoma (FA-LBCL) is a rare Epstein-Barr virus (EBV)-associated B-cell neoplasm typically arises within chronic fibrin deposits in confined anatomical spaces, whether natural or acquired. It is most commonly reported in association with cardiac myxomas, vascular prostheses and organizing hematomas. Here, we describe the first documented case of FA-LBCL arising within a hepatic cystic lesion. A 69-year-old immunocompetent man was found incidentally to have a large cystic mass in the right hepatic lobe without contrast enhancement on imaging. The lesion was surgically resected. Histologic examination revealed scattered aggregates of large atypical B lymphocytes embedded in abundant fibrin and necrotic material without invasive growth. Tumour cells were positive for pan-B cell markers CD20 and CD79α, exhibited a MUM1 index of approximately 50%, demonstrated a high proliferative index, and tested positive for Epstein-Barr virus-encoded RNA (EBER) by hybridization, supporting the diagnosis of FA-LBCL. The patient received no additional treatment and remained recurrence-free at 9 months' follow-up. This report reviews the literature on FA-LBCL, emphasizing clinicopathologic features, proposed pathogenesis, and key differential diagnoses. This case broadens the anatomic spectrum of FA-LBCL, and emphasises the need for heightened awareness of this condition when it occurs in uncommon sites to avoid misdiagnosis.