Breast cancer is malignant because cancer is a common term for malignant tumors, which are also malignant tumors originating from epithelial cells, referred to as cancer, including breast cancer, thyroid cancer, stomach cancer, colon cancer, rectal cancer, etc. If it originates from mesenchymal tissue, it is usually called sarcoma, such as osteosarcoma, etc. Therefore, as long as it is breast cancer, it means it is a malignant tumor. For malignant tumors, even if they are found early, they are more likely to have metastasis and recurrence after surgery, because the growth of malignant tumors is invasive, usually with unclear borders and hard texture, and the worse the differentiation, the greater the probability of metastasis or the risk of metastasis, so for malignant tumors, early diagnosis and early treatment are needed. Breast cancer is mostly malignant and usually requires timely radical surgery with postoperative comprehensive treatment to improve the cure rate and reduce the risk of recurrence and metastasis.