Multiple tiny solid nodular foci in the lungs seen on CT of breast cancer are not necessarily metastatic, but can also be primary lung cancer or benign nodules. 1. Breast cancer metastasis, lung metastasis may occur when the disease develops to middle or late stage, and the multiple tiny nodules often have no obvious symptoms, and when the nodules progress further, coughing and other manifestations will appear, and chemotherapy is often needed at this time. 2. Primary lung cancer, although the patient suffers from breast cancer, lung nodules may be primary lung cancer, which cannot be differentiated only by clinical manifestations and needs to be confirmed by puncture examination. 3. Benign lesions, the multiple lung nodules may be benign changes without clinical manifestations.