Breast cancer is one of the most common malignant tumors in women. Its development is often genetically related, and its incidence is higher in women between the ages of 40 and 60, before and after menopause. The earliest manifestation of breast cancer is a small, painless, progressive, solitary lump in the affected breast. The lumps are most commonly found in the outer upper quadrant, followed by the nipple, areola and inner upper quadrant. The lumps are often found unintentionally (e.g., bathing, dressing) because there are no conscious symptoms. A small number of patients may have varying degrees of tenderness or irritation and nipple discharge. The growth rate of the lump is fast, and invasion of the surrounding tissues may cause changes in the shape of the breast and a series of physical signs. For example, the skin on the surface of the tumor may be sunken; the cancerous tumor adjacent to the nipple may draw the nipple toward the cancerous tumor; the nipple may be invaginated, etc. If the cancer is larger, it can make the whole breast tissue contract and the lump protrude obviously. If the cancer continues to grow, it will form the so-called “orange peel-like” changes. These are the important signs of breast cancer. Lymphatic metastasis of breast cancer is mostly manifested as enlarged lymph nodes in the ipsilateral axilla, which are scattered, painless, hard, less in number and can be pushed; later on, the number of enlarged lymph nodes increases and adhere to each other to form a mass, which is fixed by adhesion with skin or deep axillary tissue. Few patients may have contralateral axillary lymph node metastasis. In case of distant metastasis of breast cancer, chest pain, shortness of breath and pleural fluid may appear when it reaches the lung; in case of vertebral metastasis, severe pain or even paraplegia may appear; in case of liver metastasis, jaundice and hepatomegaly may appear. When breast cancer develops to advanced stage, skin invasion on the surface may lead to skin hard nodes, or even skin ulcers. If the cancer invades deeper, it may invade the pectoral fascia and pectoral muscle, resulting in the lump being fixed in the chest wall and not easily pushed. It should be noted that some special forms of breast cancer (such as inflammatory breast cancer and eczema-like carcinoma of the nipple) have different developmental patterns and clinical manifestations from those of general breast cancer.