Non-bacterial Thrombotic Endocarditis in a Patient With Squamous Cell Carcinoma of the Lung: Diagnostic Challenges and Management Perspective.

Non-bacterial thrombotic endocarditis (NBTE), also known as marantic endocarditis, is a rare entity characterized by sterile vegetation on cardiac valves. It is typically associated with underlying hypercoagulable conditions, such as a patient with malignancy or autoimmune disease. We report a 70-year-old patient who presented with chronic cough, intermittent fever, progressive dyspnea, and significant weight loss. Imaging revealed left-sided pleural effusion with lung collapse, and further evaluation identified a central bronchial mass consistent with squamous cell carcinoma of the lung with liver metastasis. Transthoracic echocardiography demonstrated a 13-mm vegetation on the anterior mitral valve leaflet, initially raising suspicion for infective endocarditis. However, multiple blood cultures remained persistently negative, and there was no clinical or radiological evidence of systemic embolization. Despite prolonged empirical antibiotic therapy, vegetation persisted unchanged. In the context of underlying malignancy, a diagnosis of NBTE was established. Anticoagulation was deferred due to recurrent hemoptysis associated with the bronchial tumor. Overall, this case highlights the need for broader diagnostic thinking beyond infective etiologies when evaluating cardiac vegetation, especially in patients with systemic features suggestive of malignancy.