From lung to heart: An unusual voyage of primary pulmonary diffuse large B-cell lymphoma with left atrial invasion – Unmasking a diagnostic enigma and redefining clinical rarity

Abstract: Primary pulmonary lymphoma is an uncommon entity, accounting for <1% of all non-Hodgkin lymphomas and <0.5% of primary lung tumors. Cardiac extension via the pulmonary vein is exceptionally rare. We report a case of a 55-year-old postmenopausal female with hypothyroidism and rheumatoid arthritis who presented with progressive dyspnea and significant weight loss. Imaging revealed a large fluorodeoxyglucose-avid mass in the right lower lobe of the lung extending into the left atrium with tumor thrombus, mediastinal lymphadenopathy, and adrenal involvement. Histopathology and immunohistochemistry confirmed diffuse large B-cell lymphoma (DLBCL) with a high proliferative index (Ki-67: 95%). This case emphasizes the importance of comprehensive imaging and immunophenotyping in diagnosing atypical thoracic masses.