Epstein-Barr Virus–Negative Fibrin-Associated large B-cell lymphoma arising in an atrial Myxoma: A case report

Introduction Primary cardiac tumors are rare, with lymphomas representing a small subset, most often diffuse large B-cell lymphoma (DLBCL). Fibrin-associated large B-cell lymphoma (FA-LBCL), newly recognized as a distinct entity in the 2022 World Health Organization (WHO) classification, typically arises in fibrin-rich, immune-privileged spaces and is usually Epstein–Barr virus (EBV)-positive. Case Presentation We describe a 50-year-old female who presented with progressive dyspnea and palpitations and was found to have a 6-cm left atrial mass attached to the interatrial septum. Surgical excision revealed a myxomatous lesion with fibrin deposition harboring large atypical B cells. Immunophenotyping confirmed EBV-negative FA-LBCL with a Ki-67 index approaching 100% and probable BCL6 rearrangement. Next-generation sequencing identified pathogenic PIM1 and ETV6 mutations. No adjuvant therapy was administered. The patient has remained disease-free over a 24-year follow-up period. Conclusion This case illustrates an indolent EBV-negative FA-LBCL arising within an atrial myxoma, successfully managed with surgery alone and demonstrating exceptionally durable remission. High-level MGMT promoter methylation suggested a possible EBV “hit-and-run” pathogenesis, underscoring the biologic heterogeneity of FA-LBCL.