In clinical practice, we often encounter two types of patients. One type of patient has a history of hepatitis B, and the tumor marker AFP (alpha-fetoprotein) is found to be mildly elevated in the physical examination of the unit. At this time, patients are often anxious and subjectively believe that they have liver cancer, so they are in a panic and have difficulty sleeping and eating. Another group of patients, who have a history of breast cancer and have undergone surgery and post-operative chemotherapy, have persistently elevated tumor marker CA153 in outpatient checkups and are recommended to be hospitalized. Then, what exactly is the meaning of tumor markers? What is the significance of checking tumor markers? We are going to talk about this issue today. What is a tumor marker? Long-term medical practice proves that early diagnosis is the key to cure tumors. The earlier the tumor is detected, the better the treatment effect and the more treatment means. However, at present, tumors that can be detected by MRI, CT, X-ray imaging or under the direct view of endoscope have grown into certain masses, which are not yet up to early detection. Once malignant tumors develop, patients often deteriorate, especially in late stage, and the prognosis is poor. It has been the goal of clinical research for oncologists to find out how to detect cancer when it occurs in normal cells. In essence, malignant tumor is the result of genetic mutation of normal cells in the body, which becomes uncontrolled proliferation and growth. After normal cells become cancerous, cancer cells can appear antigens, proteins, enzymes, glycoproteins and polyamines that normal cells do not possess, and these substances are gradually released into the blood. Some of these substances are not present in the adult body and are only seen in the embryonic period; others are present in the normal body but in weak amounts and only exceed normal values when a tumor develops. The presence of tumors in the body can be determined by detecting these trace substances in the blood and monitoring the changes in these substances. The detection of these substances in body fluids, which can be used to assist in the diagnosis, treatment monitoring and efficacy of tumors, is called “tumor markers”. Therefore, tumor marker test is necessary for annual health checkup. The three major meanings of tumor marker testing are 1, good for early screening of tumor, and good tumor markers have some general significance in tumor screening. Medical oncologists can screen tumor patients through the detection of tumor markers in high-risk groups. For example, the detection of alpha-fetoprotein (AFP), which has special significance in the diagnosis of primary liver cancer, has become a tool for screening hepatocellular liver cancer among hepatitis B. Since the 1970s, our country has detected many liver cancer patients, especially small liver cancer patients, through AFP screening in a large number of high-risk groups in Qidong, Jiangsu Province. In addition, prostate-specific antigen (PSA) testing in elderly men can also achieve the same effect for screening prostate cancer patients. Therefore, tumor marker testing is of great value for tumor screening of high-risk groups. 2. It is helpful to distinguish the nature and biological characteristics of tumors. When a patient is found to have an occupying mass in the body by ultrasound or chest X-ray, the tumor markers in the blood can be detected to help identify whether it is a benign or malignant tumor. When a patient has a history of hepatitis B and the tumor marker AFP (alpha-fetoprotein) is found to be mildly elevated on physical examination, and the AFP still continues to be elevated monthly on follow-up, primary liver cancer can be highly suspected and further imaging or puncture pathology is recommended. In addition, the basal level of tumor markers for the first time also indirectly reflects the biological characteristics of the tumor. The higher the basal index, the greater the tumor load, the rapid development, the more tumor markers secreted into the blood, and the worse the prognosis. This is the most favored application value of tumor markers by clinical oncologists. After tumor patients are treated, the rise and fall of tumor markers have good correlation with the efficacy and prognosis of patients. Elevated tumor markers before surgery and decreased after surgery indicate successful surgery; decreased after surgery and continued to increase after a period of time suggest recurrence or metastasis of tumor. Moreover, tumor markers are particularly sensitive, and this indication often precedes the appearance of clinical symptoms by several months. Therefore, doctors often ask patients to follow up the changes of tumor markers regularly, so as to keep abreast of the development of patients’ disease and take intervention measures early. Similarly, the decrease of tumor markers after chemotherapy for tumor patients indicates that chemotherapy is effective; if tumor markers continue to increase after treatment, the chemotherapy regimen should be changed. If tumor markers continue to increase after changing the chemotherapy regimen, it often indicates that the tumor has become resistant to conventional chemotherapy drugs, which indicates the recurrence or metastasis of the tumor. What are the common tumor markers? At present, there are more and more tumor markers that have been tested in clinical practice. AFP is produced by the yolk sac and embryonic liver and reaches its peak in the 5th month of gestation and decreases at birth. One year after the birth of the fetus, serum AFP should drop to normal adult levels. After hepatocellular carcinoma, high level of AFP can be produced, therefore, if serum AFP>400μg/L or AFP increases gradually from low to abnormal, liver cancer can be highly suspected, and its positive diagnostic rate can reach 70%-90%. In addition, AFP can also be elevated in patients with ovarian cancer, but it is rare in gastrointestinal cancer and lung cancer; it can be elevated transiently in pregnant women; it can also be moderately elevated in the serum of patients with chronic hepatitis and liver cirrhosis. In patients with metastatic liver cancer, AFP is usually not elevated. 2.Cancer embryonic antigen (CEA) is a glycoprotein present in colon cancer and embryonic colonic mucosal epithelial cells. Normal human serum CEA <30μg/L. Elevated CEA is mainly seen in colon cancer, but also in pancreatic cancer, breast cancer, lung cancer, etc. Therefore, CEA is not significant as a diagnosis, but as an indicator for clear diagnosis and regular follow-up, it can help analyze the efficacy, judge the prognosis and predict the recurrence or metastasis of tumor. In addition, mild elevation of CEA in physical examination may also be caused by chronic gastrointestinal inflammation. CA19-9 is a glycolipid with no organ specificity and is elevated in many adenocarcinomas, such as pancreatic, lung, colon and gastric cancers, among which the sensitivity is higher in pancreatic, gastric and bile duct cancers. 85%-95% of patients with pancreatic cancer have a high level of this index, which is a more reliable marker of pancreatic cancer. CA19-9 is a reliable marker of pancreatic cancer. CA19-9 measurement can help to judge the prognosis, and its prediction of recurrence and metastasis is often found before radiological examination. CA12-5 is a marker of epithelial ovarian cancer and endometrial cancer. Pancreatic cancer, hepatocellular carcinoma, breast cancer and endometritis, acute pancreatitis, peritonitis, hepatitis and cirrhotic ascites can also elevate CA12-5. Elevated CA12-5 is also associated with tumor recurrence. Therefore, it helps to follow up the disease. 5.CA15-3 is secreted by secretory epithelial cells (such as those of breast, lung, gastrointestinal tract and uterus). Although this antigen is not organ- and tumor-specific and has elevated indicators in breast, lung, prostate, ovarian and gastrointestinal cancers, it has a higher correlation with breast cancer. Therefore, it is mainly used to determine the progression and metastasis of breast cancer, monitor treatment and recurrence. 6.Prostate specific antigen (PSA) is a serine protease, a glycoprotein, found in prostate and semen extracts, and is a specific marker of prostate cancer. PSA is <2.5 μg/L in normal men and is significantly elevated in prostate cancer. Each "tumor marker" has its own usefulness and limitations. The diagnostic sensitivity and specificity of each tumor marker are different and should be tested under the guidance of a clinician. If necessary, several markers can be combined to improve the diagnostic efficiency. It is important to emphasize that a mild elevation of a single marker may also be caused by benign diseases. It should not be considered as malignant tumor on this basis, and the differential diagnosis should be carefully based on the comprehensive examination of the patient. With the progress of molecular biology and human genome project, more and more specific tumor markers have been discovered and applied, providing a new way for early diagnosis of tumors.