Tumor biopsy “gold standard” is very confusing Cancer is one of the main causes of life threatening diseases, the probability of Chinese people getting cancer in their lifetime is 22%, and 5 people die from cancer every minute. At present, cancer examination is a comprehensive judgment through clinical symptoms, imaging and histopathological analysis, while the clinical symptoms are complex and the current imaging equipment can only detect the occupying lesions as small as 1-3 cm in diameter. However, it requires surgery to take samples from local tissues for pathological examination. Obviously, it is very difficult to get biopsy tissues for smaller tumors, and to wait for tumors to increase before examination will definitely delay the diagnosis and early treatment of the disease, and most of the clinically diagnosed cancers are in advanced stage. On the other hand, biopsy methods cannot monitor changes in primary tumors over time, and biopsy causes a lot of pain to patients, making it infrequent for examiners to sample metastatic sites. Although biopsy sampling is not thought to cause cancer cell spread, recent studies have shown that surgery or biopsy wounds may lead to tumor progression, and noninvasive diagnosis of tumors has been the idealized solution for early clinical diagnosis, personalized treatment, and treatment prognosis check. The ideal of tumor markers is very rich. Cancer cells abnormally transcribe, express, secrete or release some related substances during the process of occurrence, proliferation, differentiation, metastasis and necrolysis, etc. The body will also abnormally produce or up-regulate some physiological substances in response to the existence and growth of tumor, mainly including proteins, peptides, hormones, enzymes, polyamines, oncogene products, viral antigens, free cells, etc. Their existence or quantitative changes can indicate the nature of tumor. can indicate the nature of the tumor. These substances can be measured by biochemistry, immunology, molecular biology and cell biology with advanced instrumentation, and signals closely related to tumor activity can be determined as tumor markers. Tumor markers are used to identify cancer type, determine cancer stage, predict cancer growth rate, determine therapeutic target, select drug response, observe treatment effect, monitor recurrence and prognosis evaluation. Tumor marker testing is the only way to detect asymptomatic microfocal tumors at an early stage. The ideal tumor markers should have the following characteristics: 1. High sensitivity: easy to detect in body fluids, especially in blood, can detect tumor at very early stage, low false negative not to miss diagnosis; 2. High specificity: that is, normal human tissues do not secrete, different tumors have corresponding tumor markers, false positive not to misdiagnose; 3. Localizable: with organ specificity, can be used to determine the location of lesions; 4. Quantitative. The determination method is precise and accurate, easy to operate, and the level in body fluid should be closely related to the size of tumor and clinical stage; 5. Pathologically relevant: it can be used to judge tumor progression, efficacy, prognosis and recurrence; 6. Short half-life: it can reflect the dynamic changes of tumor and monitor the treatment effect, recurrence and metastasis. Tumor markers reality is very skeletal Scientists spared no efforts to find tumor markers, pouncing on every bright spot in the dark night and catching every trace, from proteins to glycans, from DNA to RNA, from hormones to isozymes, from genome to metabolome, from transcriptome to metabolome, from signal transduction to epigenetics. after 1928, numerous tumor markers such as oncoproteins, hormones, enzymes oncogenes, miRNA, lncRNA, ctDNA, circulating tumor cells and other tumor markers have been discovered one after another and used for clinical testing, and new tumor markers are still being discovered. However, it must be admitted that the clinical application of these markers is very limited: low sensitivity: although tumor marker examination has been widely used in clinical practice, the sensitivity and specificity of the tumor markers used are limited, and the positivity rate for early stage of tumor (stage I and II) is low, and no tumor marker has been found to replace the “gold standard” of pathological examination. The sensitivity and specificity of single tumor markers are limited. The results of a single tumor marker test cannot be used as a basis for tumor diagnosis. 70% of people with elevated AFP do not have liver cancer in their final test results. Also, a negative tumor marker test does not necessarily rule out tumors, as there are false positives or false negatives. Tumor markers are generally not used for medical checkups of normal people, otherwise there may be greater mental stress for those who have false positives. Poor specificity: Tumor markers do not correspond to tumors one by one, because the same tumor may contain one or more tumor markers, and different tumors or different tissue types of the same tumor may have common tumor markers or different tumor markers. A positive tumor marker test is not necessarily a tumor, but only a hint and signal, which needs to be combined with the patient’s medical history, symptoms, physical examination and imaging examination to make a comprehensive judgment. For example, certain benign diseases, certain physiological changes (e.g. pregnancy and menstruation) and autoimmune diseases such as lupus erythematosus and glomerulonephritis have mostly positive reactions for tumor markers; therefore, a combination of tumor marker tests are used clinically to improve sensitivity. It cannot be localized: the organ and tissue specificity of tumor markers is usually poor; therefore, a diagnostic specificity of more than 80% is already a marker with good specificity, but because the prevalence of tumors in the population is low, thus tumor markers have a low positive prognostic value if detected by qualitative methods. In other words, the false-positive rate will be high if a patient’s presence of tumor is determined by negative or positive tumor marker test alone. The diagnosis of tumor must be based on histopathology or cytopathology. Due to the individual differences of patients and their specific clinical conditions, the analysis of tumor markers should be combined with clinical conditions and compared from multiple perspectives in order to reach an objective and true conclusion. Lack of predictiveness: Tumor markers, because of their low specificity, can basically only be used for tumor efficacy observation as well as treatment and recurrence monitoring. Combined testing should not be used for the purpose of tumor diagnosis, but as a method to screen for markers that can sensitively indicate efficacy as well as treatment and recurrence before treatment of tumor patients. This is because if individual tumor markers do not have the value to diagnose tumors specifically and sensitively, it is also not possible to have an ideal mode of combination application that is specific and sensitive to a particular tumor. However, there are some tumor markers for which combined testing is meaningful for specific tumors, such as AFP, HCG and lactate dehydrogenase for testicular cancer diagnosis/case finding, disease staging, prognosis, recurrence and treatment monitoring. aFP can also be used to differentiate between non-seminomatous and seminomatous cell tumors. Lack of consistency: malignancies may not be consistent in their ongoing development, and certain markers may be present from the beginning to the end. The expression of a marker varies significantly from patient to patient in the same type of tumor, in different cell populations of the same tumor, and at different times in the growth of the same population, and can vary widely from a high phenotype to a complete absence. This phenomenon is called heterogeneity of tumor antigen expression. The overall need for localized local tissues during carcinogenesis has some genes turned off and some genes turned on. This change in timing is not completely synchronized in different cells. Different cell groups have their own signs and pathways at different growth stages, and the process of tumorigenesis and development can present a multi-gene regulation and multi-molecular expression phenotype. False Positive False Negative: Most markers are products of cell proliferation or hyperplastic cells, which can also be positive or even have high values in normal physiological state. For example, CEA can be high in pregnant women, in the smoking population, and even higher in many non-cancerous pathological states. Another example is CA19-9 is high in the serum of patients with cirrhosis; however, those who are negative are cancerous. The positive rate of most tumor markers in the serum of patients is generally 30% to 40%, mostly not more than 60%, even in advanced cases. In many tumor tissues, none of the cancer cells contain the markers at all. This indicates that these markers are not a marker for that type of tumor, not its essence. If the positivity rate is not high, the result is that cancer cannot be detected, which kills people; if the specificity is not good, the result is that what is detected is not cancer, which scares people to death. Lack of standardization: Tumor markers are mostly proteins with complex structures or glycoantigenic epitopes that can only be determined by antibodies. Different laboratories use different antibodies, different sensitivity and specificity of detection methods, or the same research group uses the same method to study different tumors, and the final markers obtained are very different. Then, different research groups study different tumors with different methods, and what they come up with is even more massive data and results, which cannot lead to accurate conclusions, leading to the limited practical application of thousands of tumor markers reported in the literature now. The dream of tumor markers is distant. There are so many tumor markers but still none of them can replace pathological examination as the gold standard for tumor diagnosis. As pointed out by Academician Fan Daiming, hundreds of billions of dollars have been spent on research to find ideal tumor markers, tens of thousands of molecules have been discovered, hundreds of thousands of conferences have been held, and millions of papers have been published, but nearly ten million patients still die every year as a result. It seems that the more attention people pay and the more work they do, the further away from real application they seem to be, and the further away from the truth they seem to be. On the one hand, those who are new to the field seem to feel that there is no future; on the other hand, those in authority seem to feel that there is nothing they can do.