━━ Background. Thrombotic complications associated with coronavirus disease 2019 (COVID-19) vaccination have been reported. We herein report a resected case of lung cancer with pulmonary thromboembolism after COVID-19 vaccination. Case. A 74-year-old man visited our hospital three days after his second COVID-19 vaccination due to breathlessness. Plain chest CT showed only a mass in the left upper lobe. Nine days after vaccination, his symptom worsened and he visited our hospital again. His

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... ation of percutaneous oxygenation (SpO2) was 89%, and his D-dimer level was 25.9 μg/ml. Contrast-enhanced CT revealed thrombosis of the bilateral pulmonary arteries and left popliteal vein. Apixaban was administered, and his symptom improved. His D-dimer level decreased to 7.4 μg/ml. The left upper lobe nodule was diagnosed as lung cancer. After the disappearance of thrombus and normalization of the D-dimer value, we performed thoracoscopic resection of the left upper lobe. The vessel sheath of the pulmonary artery had thickened and was difficult to peel off. The patient is currently alive without relapse of thrombosis. Conclusion. Although thrombotic events after COVID-19 vaccination are rare, high rates of severe disease and mortality have been reported. The number of cases involving lung cancer patients with adverse events related to COVID-19 vaccines will increase in the future. Thus, the elucidation of the pathophysiological mechanism and establishment of effective treatment policies are expected.