Breast cancer with fever may be combined with upper respiratory tract infection, or it may be tumor fever caused by advanced stage of breast cancer or fever caused by brain metastasis of tumor cells. 1. Breast cancer combined with upper respiratory tract infection: due to the decrease of breast cancer patients’ own immunity, they are easy to be attacked by bacteria or viruses, resulting in upper respiratory tract infection, and then they may have fever. 2. Tumor fever: at the advanced stage of breast cancer, due to the enlargement of tumor, there may be a lot of necrosis of tumor cells, and in the process of absorption of cancerous substances, fever may also occur, which belongs to tumor fever. 3. Brain metastasis: If brain metastasis occurs in the late stage of breast cancer, the tumor cells will be transferred to the hypothalamus thermoregulation center, which may cause central fever, manifesting as high fever. If breast cancer is accompanied by fever, it is recommended to cooperate with professional doctors for examination as soon as possible to clarify the cause of fever and take effective treatment measures in time to avoid aggravation of the condition.