CA15-3, whose full name is glycoantigen 15-3, is a tumor marker commonly used in clinical practice. The sensitivity of CA15-3 in breast cancer patients with elevated CA15-3 is about 60% in the early stage of breast cancer and about 80% in the late stage of breast cancer.CA15-3 is valuable for the observation of the efficacy of breast cancer, prognosis, as well as the diagnosis of recurrence and metastasis.The dynamic measurement of CA15-3 is helpful for the early detection of recurrence after treatment in stage II and III breast cancer patients. The dynamic measurement of CA15-3 is helpful for early detection of recurrence after treatment in stage II and III breast cancer patients. When CA15-3 is greater than 100 U/ml, metastatic lesions can be considered. In addition, malignant tumors in other sites such as ovarian cancer, pancreatic cancer, and cervical cancer may also show elevated CA15-3. Some other clinical diseases of the gastrointestinal tract or liver, breast or ovary may also have elevated CA15-3.