Incidentally Discovered Endocarditis Leading to the Diagnosis of an Epidermal Growth Factor Receptor Mutant Metastatic Pulmonary Malignancy of Occult Primary Tumor

INTRODUCTION: Non-bacterial thrombotic endocarditis is well documented in the literature to occur in patients with known malignancies. It is, however, much less common for patients to be diagnosed with marantic endocarditis as the presenting sign of an unknown primary malignancy. CASE PRESENTATION: We discuss a case in which a patient was undergoing routine surveillance for his known heart failure with a transthoracic echocardiogram when an aortic valve vegetation was discovered. After further investigation, he was found to have metastatic adenocarcinoma of the lung. Next-generation sequencing was utilized to identify an EGFR mutation, which led to the patient being treated with osimertinib. CONCLUSION: Adequate treatment of his primary malignancy, along with anticoagulation, led to overall clinical improvement of the patient.