After people suffer from breast cancer, the causes of new single solid nodule in lungs include tumor lung metastasis, lung infection and so on. It is suggested that people should go to regular hospitals for further examination to clarify the causes of the disease and treat the cause under the guidance of doctors. 1. Lung metastasis: the most common target organ for breast cancer metastasis is lung. If there is a new single solid nodule in the lung, it is likely to be breast cancer lung metastasis. It is recommended to take biopsy pathology under doctor’s guidance to clarify the cause of the disease and carry out treatment. 2. Lung infection: when lung abscess is formed due to viral or bacterial infection in the lungs, it will show lung nodules in the lungs during CT, chest X-ray and other imaging examinations. It is recommended to carry out blood and sputum specimen examination to clarify the causative organisms, and carry out anti-infection medication (e.g. cephalosporin, etc.). Or in the case of tuberculosis, imaging tests such as CT or chest radiographs show scattered nodules in the lungs.