Tumor markers are specific products of tumor cells, biochemical substances that indicate the presence of tumors and reflect their certain biological characteristics. From the clinical point of view, they mainly refer to those tumor-related substances that can be detected in blood, body fluids and tissues. In recent years, on the one hand, the incidence of various tumors is increasing due to various reasons, on the other hand, with the improvement of living standard, “living well, being healthy” has become the consensus of people, and health checkups have received unprecedented attention, and some tumor markers have been included in the items of health checkups. Doctors often prescribe some tumor markers for patients to test, hoping to detect tumors at an early stage. However, in fact, most of the tumor marker tests cannot achieve the purpose of early tumor diagnosis. This article only discusses and analyzes the clinical selection of tumor markers and the common misunderstanding. In fact, except for AFP, which is useful for the early diagnosis of primary liver cancer, and PSA, F-PSA and their ratios, which are useful for the early diagnosis of prostate cancer, other tumor markers are not of great significance for the early diagnosis of tumor, and their clinical value is mainly reflected in the analysis of efficacy, prognosis and prediction of recurrence and metastasis. The clinical value is mainly in analyzing the efficacy, judging the prognosis, predicting the recurrence and metastasis. The early diagnosis of tumor needs to be combined with medical history, symptoms, physical signs, imaging examination (ultrasound, CT, X-ray, gastroscopy, colonoscopy), etc., and the definite diagnosis needs to rely on pathological examination. Myth 2: Negative tumor markers can exclude related tumors Since the detection of most tumor markers does not have great significance for the early diagnosis of tumors, the negative tumor markers cannot completely exclude related tumors. For example, the early stage of gastric cancer is limited to infiltration or lymphatic metastasis before serum CA199 is significantly elevated. There was once a patient around 50 years old with a history of gastric disease for more than 30 years, aggravated for two weeks, who was ordered by a gastroenterologist to undergo gastroscopy, but he refused on the grounds of recent negative CA199 and CA50 indicators. It was only after six months of jaundice but no abnormal liver function that he was forced to undergo gastroscopy, only to find that the gastric cancer was advanced and he died a month after the reluctant surgery. Even for a tumor marker like AFP, which is quite significant for the early diagnosis of primary liver cancer, its positive rate only reaches 79% to 90%, (the positive threshold for AFP to diagnose primary liver cancer is >400ng/ml). In other words, 10%-30% of patients with primary liver cancer have normal or only mildly elevated AFP. Myth 3: Abnormal tumor markers Many benign diseases can have abnormal tumor markers, for example, prostate hypertrophy and prostatitis can have mild to moderate elevation of PSA, endometriosis can have mild to moderate elevation of CA125, and acute and chronic liver diseases can have different degrees of elevation of CA125, CA199, CA50 and ferritin. Biliary tract disease with jaundice often has significant elevations in CA199 and CA50, and even long-term smokers may have mild elevations in CEA. There was once a 50-year-old simple hepatitis B surface antigen positive person whose CA199 had been hovering between 50 and 70u/ml, (normal reference value <37u/ml), without any other abnormalities in the systemic examination, for more than ten years now. Myth 4: Tumor markers are highly efficient as long as they are combined The combined application of tumor markers can indeed improve the positive detection rate to some extent, but the correlation between some tumor markers is extremely high, for example, the correlation between CA199 and CA50 can reach 95% to 98%, that is, 95% to 98% of the subjects with normal CA199, then CA50 is also normal, CA199 is abnormal, then CA50 is also abnormal. For example, CA242 is less affected by jaundice and has a higher value in the differential diagnosis of benign and malignant diseases of the biliary tract and pancreas. Myth 5: Mild elevation of tumor markers is of little value Just because many benign diseases can have abnormal tumor markers, some doctors think that mild elevation of tumor markers is of little value, and it is only meaningful if it is more than 5 times higher than the normal reference value. This is not true because in most cases, the range of normal reference values is set relatively wide. Therefore, even a mild elevation of a tumor marker can be of great value after excluding benign disease. There was a patient whose CA199 and CA50 were only mildly elevated, and after repeated examinations, gallbladder cancer was finally detected by enhanced CT, and he has survived for 3 years after timely surgery.