Lung adenocarcinoma initially presenting as Trousseau's syndrome treated successfully with pembrolizumab: A case report

A 60‐year‐old woman was urgently admitted to our hospital because of vertigo and left hemiplegia. Laboratory examination showed thrombocytopenia, high levels of D‐dimer and carcinoembryonic antigen. Brain magnetic resonance imaging (MRI) revealed multiple bilateral cerebral infarctions. Chest computed tomography (CT) showed an irregularly shaped tumor in the upper lobe of the left lung and mediastinal node swelling. The histopathological findings revealed adenocarcinoma negative for anaplastic lymphoma kinase fusion gene, sensitive epidermal growth factor receptor mutations. A diagnosis of lung adenocarcinoma initially presenting as arterial thromboembolism was made, and she was treated with direct oral anticoagulant (DOAC). Subsequently, pembrolizumab therapy was initiated because tumor cells were positive for programmed cell death protein 1 (PD‐L1;60%), and resulted in reduction of the tumor with normalization of the platelet count and d‐dimer. The treatment has been continued for over one year without any recurrence of the disease or thromboembolism.