A patient with a lung adenosquamous carcinoma harboring a de novo T790M mutation and huge nonbacterial vegetative growths successfully treated with osimertinib: A case report

Nonbacterial thrombotic endocarditis (NBTE) is a rare condition; sterile vegetations attach to heart valves. NBTE is typically found in patients with malignancies or autoimmune disorders. Although surgical interventions are sometimes performed, the appropriate indication and timing are still unclear. Here, we describe a 72‐year‐old woman diagnosed with adenosquamous carcinoma of the lung. She was initially diagnosed as pT2aN0M0 and underwent RUL lobectomy. After nine months, lung cancer recurred, and she underwent treatment with cytotoxic chemotherapy. However, images showed progression after only one month. Rebiopsy revealed she had comutation of de novo EGFR L858R and T790M. Treatment was changed to gefitinib. After one month, she experienced loss of consciousness. Brain magnetic resonance imaging (MRI) showed multiple lesions resembling infarctions or metastases. Chest computed tomography (CT) revealed progression. Osimertinib was prescribed and she underwent echocardiography to rule out the possibility of a cardiogenic embolism. Surprisingly, severe mitral regurgitation and a massive vegetation on the mitral valve were found. Cardiologists recommended surgery due to the severity of the embolic event and valve dysfunction, but it was decided to continue antibiotics, osimertinib, and anticoagulants instead of surgery due to the patient's poor general condition and the possibility of NBTE. Six weeks later, the patient's condition markedly improved and echocardiography revealed a marked reduction in vegetation size. Clinicians should be aware that targeted therapy can be effective in treating severe cancer complications, such as NBTE, as evidenced by the successful treatment of lung cancer with osimertinib. This option should be considered, particularly for elderly lung cancer patients, before resorting to surgery as a first‐line treatment for NBTE.