Multiple small nodules in both lungs of breast cancer may be due to metastasis of breast cancer, which is more serious; in addition, benign diseases such as pneumonia and tuberculosis are also easy to cause multiple small nodules in lungs. 1. Breast cancer metastasis: Multiple small nodules in both lungs of breast cancer patients may be due to breast cancer metastasis. Metastasis of malignant tumors is often more serious, and if the treatment is not timely, it may seriously damage the lung function, and multi-organ metastasis may occur, resulting in serious damage to the patient’s body function and affecting the patient’s life span, so the patient should undergo timely treatment. 2. Benign diseases: Pneumonia, tuberculosis and other diseases will also be manifested as multiple nodules in the lungs, and sometimes patients will have fever, cough, coughing up blood, coughing up sputum and other symptoms; when the disease is serious, it will lead to respiratory difficulties and other symptoms. When breast cancer patients have multiple nodules in both lungs, they should be diagnosed in time and treated according to the cause of the disease.