Glycoantigen 15-3 is a tumor marker in human body, if the content of Glycoantigen 15-3 in human body exceeds the normal standard range, it indicates that there are tumors in human body, which means that the presence of breast cancer in human body indicates that human body’s immune system has been impaired, human body’s immune system has been reduced, and the content of various kinds of immune cells, such as leukocytes and neutrophils, has been decreasing. Glycoantigen 15-3 is not only a tumor marker for breast cancer, but also a tumor marker for lung cancer, colon cancer and ovarian cancer, which means that tumor factors have already appeared in the human body, which should be treated in time to prevent them from metastasizing throughout the body along with the bloodstream and the lymphatic system, and at the same time, Glycoantigen 15-3 is a marker for patients who are undergoing cancer treatments to check whether the cancer treatments are effective or not.