Mammaglobin is a glycoprotein secreted by epidermis, which is a specific protein of mammary gland. Mammaglobin gene is located in a dense gene cluster of 11q12.2. In normal tissue, it is only expressed in mammary duct and lobular epithelial cells. In primary breast cancer, the expression rate is 80%, with high specificity and sensitivity, and it is an ideal marker for micrometastasis of breast cancer.