Breast cyst 4a, generally referred to as BI-RADS classification IVa. Complex breast cyst IVa, which carries some risk of malignancy, can also be seen in benign breast cysts and therefore cannot be judged to be serious. Complex breast cysts IVa are categorized according to the nature of the breast disease by ultrasound examination. Class I-III are almost always benign, while class IV and above have the possibility of malignancy. If a complex breast cyst is found to be IVa, it is recommended that a puncture biopsy be performed to clarify the nature of the cyst. Patients with benign cysts may have limited dilatation of breast glands or ducts and cystic secretion, which can be observed for the time being. Patients with malignant breast cysts may have bloody nipple discharge and require early surgical treatment. Complex breast cyst IVa may be more malignant if there are breast cancer patients in the patient’s family, so close attention must be paid to it. Patients with complex breast cyst IVa need to pay enough attention to the fact that patients with benign biopsy still need to be followed up regularly, and patients with malignant biopsy need to cooperate with doctors for active treatment.