Intrapulmonary metastasis is a malignant tumor from any part of the body that has moved to the lung through blood circulation, lymphatic system and direct infiltrative transfer, and it is an advanced manifestation of malignant tumor. The lung is a common site of metastasis for malignant tumors, and the frequency of metastasis occurrence is related to the patient’s disease progression and the natural course of the particular tumor. Malignant tumors that occur within or outside the thorax of the lung can metastasize to the lung through four pathways: 1. hematogenous metastasis. 2. lymphatic metastasis. 3. direct invasion. 4. intratracheal metastasis.