Malignant tumors metastasize to the lungs mainly through hematogenous diffusion, and tumor emboli obstruct the pulmonary vasculature leading to pulmonary vascular embolism. Compared with thromboembolism, it is more difficult for tumor emboli to show vascular recanalization and gradually form irreversible obstruction of the pulmonary vascular bed. Pulmonary tumor embolism manifests itself in four types of pulmonary vascular involvement: 1. large tumor emboli obstructing proximal pulmonary arteries; 2. tiny tumor emboli invading pulmonary vessels causing pulmonary vasculopathy (more common); 3. cancerous lymphangitis; 4. coexistence of the above three manifestations. It can lead to acute or progressive pulmonary hypertension and right heart failure. The most common symptom in patients with pulmonary tumor embolism is subacute progressive dyspnea. Definitive diagnosis of pulmonary tumor embolism is very difficult and lacks specific imaging features. Infection, thromboembolism, toxic side effects of chemotherapeutic agents and other pulmonary manifestations due to the tumor should also be considered. Pulmonary tumor embolism has a poor prognosis, with a median survival time of only a few weeks after diagnosis.