1.Classification of breast cyst Breast cyst is a kind of abnormal hyperplastic disease of breast tissue, there are different types such as simple cyst, complex cyst and cumulus cyst, among which simple cyst is the most common. 2.The causes of breast cyst formation are mainly endocrine disorder or breast tissue is more sensitive to hormones, and breast tissue is constantly stimulated by estrogen, which causes ductal epithelial hyperplasia and more cells in the ducts, resulting in duct extension, tortuosity and folding, and necrosis of the duct wall at the fold due to ischemia, forming cysts. 3.Clinical characteristics of breast cysts The onset of breast cysts varies in length. Single or multiple cystic masses can be felt in the patient’s breast. The cysts have clear borders and good mobility. In the case of multiple cysts, multiple nodules may be palpated, involving the whole breast or even both breasts, and there may be small cysts between the large cysts. The cysts can be filled with clear, colorless, yellowish, gray, green, or brown fluid, and can also bleed if the epithelium inside the cyst proliferates, forms papillomas or becomes cancerous, and the fluid can be bloody. If complicated by infection, it can cause adhesion of surrounding tissues and pain is obvious. Nipple discharge is partially visible when pressure is applied around the areola. Among them, cysts are rare to become malignant. 4.How should breast cysts be treated? The treatment of breast cysts is based on ultrasound-guided puncture and fluid aspiration. (1) If the aspiration is unsuccessful, it is more likely to be considered a hyperplastic nodule. Generally, the size of the cyst should be reviewed once every three to six months to observe the change in size. (2) If the aspiration is successful, but if colored fluid, such as black, bloody fluid, etc., is extracted during the aspiration, it is not excluded as a tumor and surgery should be performed instead. Or if the same cyst still recurs after two ultrasound-guided aspirations, surgical treatment should also be considered to remove the cyst with its cyst wall intact, then the cyst will not recur.