Malignant tumor is one of the diseases that seriously threaten human health, and the incidence and mortality rate are increasing year by year. According to the statistics of Chen Wanqing et al, lung cancer, female breast cancer, stomach cancer, liver cancer, esophageal cancer, colorectal cancer and cervical cancer are the main common malignant tumors in China. Lung, liver, stomach, esophagus, colorectal, female breast and pancreatic cancers are the main causes of tumor death. In the process of tumor research, various markers have been discovered, and these markers are widely used in clinical practice for early diagnosis of tumors, assessment of tumor patients’ conditions, and screening of high-risk patients, but can current tumor marker tests achieve early diagnosis? However, can the current tumor marker tests achieve early diagnosis, and is there any value of universal screening in the population? How to apply them in a reasonable and standardized way? I believe that many clinical practitioners have many doubts, but at present, there are still great controversies among scholars and different institutions in different countries, so there is no unified principle of tumor marker application. Here I would like to summarize the significance and application guidelines of several common tumor markers issued by domestic and foreign authorities. The recommendations of NACB (American Academy of Clinical Biochemistry) and EGTM (European Organization for Tumor Markers) on the clinical application of CEA in colorectal cancer: a. CEA testing is not recommended for screening of colorectal cancer. b. CEA testing before surgery for colorectal cancer patients can help evaluate the pathological status of patients and determine the treatment plan. c. CEA testing should not be performed immediately after surgery. d. After resection of liver metastases, CEA can be used as a clinical indicator. e. CEA can be performed during treatment to monitor treatment response and disease progression. Prostate-specific antigen (PSA) a. The NACB and EGTM agree with the American Cancer Society’s recommendation for the diagnosis of prostate cancer that PSA should not be used alone, but in combination with DRE for disease evaluation b. For very small tumors, PSA testing will give conflicting results and a low Cut-off value (2ng/ml) is not recommended. c. The NACB emphasizes that age- and race-specific reference ranges should be used for each PSA analytical test, whereas EGTM does not recommend the use of age-specific reference ranges. d. When the total serum PSA level is 4 to 10 ng/ml and the DRE (rectal examination) is negative, it is recommended that the percent free PSA be used to help differentiate between BPH (benign prostatic hyperplasia) and prostate cancer, subject to validation of the medical determination boundaries for free and total PSA test results in each case. e. It is recommended that blood samples be taken prior to prostate extrusion and several weeks after healing of prostatitis. AFP The National Comprehensive Cancer Network (NCCN) clinical practice guidelines for hepatocellular carcinoma, the American Association for the Study of Liver Diseases (AASLD) clinical guidelines for the treatment of HCC, the British Society of Gastroenterology (BSG) treatment guidelines, and the consensus developed by the American College of Surgeons (ACS), four international guidelines based on evidence-based medical evidence, all affirm the value of serum alpha-fetoprotein (AFP) in the early screening and The value of AFP in early surveillance, they state For men ≥ 35 years of age with HBV and/or HCV infection and a high risk of alcoholism, AFP and liver ultrasound are generally performed at 6-month intervals. For those with AFP > 400 μg/L without liver occupancy on ultrasound, care should be taken to exclude pregnancy, active liver disease, and tumors of embryonic origin in the gonads; if this can be ruled out, CT and/or MRI should be performed. If AFP is elevated but does not reach the diagnostic level, in addition to excluding the above-mentioned conditions that may cause an increase in AFP, the dynamic changes in AFP should be closely followed, the interval between ultrasound examinations should be shortened to 1-2 months, and CT and/or MRI should be performed when needed. If liver cancer is highly suspected, DSA hepatic artery iodography is recommended. Thyroglobulin (Tg) and Calcitonin The significance of serum thyroglobulin (Tg) and calcitonin in the management of thyroid cancer is confirmed in the 2012 edition of the Guidelines for the Management of Thyroid Nodules and Differentiated Thyroid Cancer and the third edition of the American Thyroid Association (ATA) Guidelines for the Management of Thyroid Nodules and DTC. The significance of serum thyroglobulin (Tg) and calcitonin in the management of thyroid cancer is confirmed in the Guidelines for the Management of Thyroid Nodules and DTC. Among the serum markers related to thyroid cancer, Tg and Calcitonin have become important markers for postoperative surveillance of DTC (differentiated thyroid cancer) and sensitive indicators for screening of MTC (medullary thyroid cancer), respectively, with good specificity and sensitivity, and are receiving increasing clinical attention. After treatment, the sensitivity and specificity of Tg detection for determining recurrence or residual DTC is highest after TSH stimulation (THS>30 mIU/L) and in the absence of Tg antibodies. In the absence of antibodies, if Tg is <0.5 ng/L after TSH stimulation, the probability that the patient is in a tumor-free survival state is 98%-99.5%. If Tg is >2ng/L after TSH stimulation, especially if it is >10ng/L or persistently elevated, Tg is a highly sensitive indicator of persistent tumor presence. The Guideline recommends that after the patient’s postoperative serum TSH level reaches the standard, Tg and Tg antibody (TgAb) testing should be performed every 6-12 months during the follow-up period to keep the serum Tg level below 2ng/ml. Tg and TgAb testing must be performed in the same way during the follow-up of DTC patients, and patients should be re-evaluated if changes occur. If there is a persistent trend of elevated Tg levels, the possibility of residual, recurrent or growing thyroid tissue or tumor should be considered and further evaluated in conjunction with other tests such as neck ultrasound. Calcitonin is an important tumor marker for MTC and correlates positively with tumor size. Serum Calcitonin levels in normal subjects should be less than 10ng/L. Serum Calcitonin levels in MTC patients are usually higher, often above 100ng/L. The degree of elevation correlates with tumor load and can be used as a specific tumor marker for MTC. The European Consensus on the Management of Patients with Follicular Epithelial Differentiated Thyroid Cancer published by the European Thyroid Association (ETA) recommends the use of Calcitonin for screening of patients with thyroid nodules. Elevated levels of carcinoembryonic antigen (CEA) found on screening and PET-CT can exclude cases of GI tumors, which are more likely to be MTC if Calcitonin levels are elevated. CA153 The NACB guidelines state that the results of numerous studies have established the advantages of CA15-3 for the detection of breast cancer metastases. It has been used in the evaluation of 60-80% of patients with metastatic breast cancer. The EGTM guidelines recommend the use of both CA15-3 and CEA to improve the sensitivity of clinical testing. The use of CA15-3 and CEA together in clinical practice can detect more patients with early recurrent tumors than CA15-3 alone. Currently CA15-3 is mainly used to monitor breast cancer activity. Future work will be to develop guidelines on the clinical significance of CA15-3 for treatment and prognostic follow-up monitoring. The EGTM guidelines recommend against the use of CA125 for mass screening of ovarian cancer and for occasional cases because of the lack of sensitivity (only 50% of stage I patients have elevated CA125) and specificity of CA125 in early stage disease. If a patient’s serum CA125 level is twice the baseline level, physical examination, TVS and CT should be performed immediately. Abnormalities in any of these tests suggest the need for laparoscopy and laparotomy. CA125 is helpful in the differential diagnosis of primary and malignant pelvic masses in postmenopausal women. Women with postmenopausal pelvic masses who have significantly elevated serum CA125 levels should be referred immediately to a surgical specialist for a complete abdominal examination, mass sampling, and omental resection and cytoreduction surgery. The rate of reduction in CA125 levels after initial cytoreductive surgery and during cytotoxic chemotherapy is used in many cases as an independent prognostic factor and to help the surgeon make an appropriate decision about whether to add chemotherapy to subsequent treatment. In 90% of cases, a 2-fold increase in CA125 levels during chemotherapy is associated with progression of the disease and indicates that chemotherapy is not effective. In 90% of cases, a 2-fold increase in CA125 during chemotherapy is associated with disease progression, indicating poor chemotherapy. However, disease progression may not be accompanied by an increase in CA125, and physical examination and imaging should be performed if possible. Squamous cell carcinoma antigen (SCCA) NACB guidelines state that SCCA results can be used with caution to monitor prognostic changes in clinical cases or to determine adjuvant therapy in high-risk patients. The SCCA test can be used with caution to monitor patients for disease recurrence. 76% of cases with persistently elevated SCCA values indicate disease progression or recurrence, with a false positive rate of 2.8-5%. 2.8 to 5%. Therefore, testing serum SCCA levels every three months in patients undergoing radiation therapy or surgery can be useful in determining their treatment plan, but there is no documented clinical use of SCCA.