CA15-3, also known as glycoantigen 15-3, is a commonly used tumor marker that may be elevated in women with breast malignancies, but is not specific. In other malignant tumors, such as ovarian malignancy and mastitis, this marker may be elevated. It can be used as an indicator for follow-up after surgery or chemotherapy for breast cancer malignancy. If this index suddenly increases more during the examination, it indicates that the disease may have progressed and further imaging examinations, including CT of the chest and abdomen, MRI of the breast, mammography, etc., are needed to understand whether there is local recurrence or distant metastasis.