The reason why malignant tumors are known as incurable diseases lies in the specificity of its onset. In the early stage of its onset, it is an invisible killer, immobile, the patient can not feel its existence and let it develop and grow; and once it shows the murder weapon, the patient has often been systemic metastasis, losing the opportunity to treat, can only be slaughtered. The treatment of malignant tumors is based on the word “early”, the earlier the discovery of malignant tumors, the better the therapeutic effect, and even can be completely cured, and once it enters the late stage, its therapeutic effect will be greatly affected. Therefore, the best treatment method for malignant tumors is early diagnosis and early treatment to kill the disease in the cradle. How to detect malignant tumors at an early stage has always been a difficult problem for scientists to overcome. Since early detection of malignant tumors often means that the patient does not have any symptoms at this time, thinking that the body is completely healthy, it is very difficult for such patients to accept any painful and potentially traumatic tests, such as the pathological biopsy necessary for the diagnosis of tumors. Various imaging tests such as CT, MRI, PETCT, etc. are relatively expensive, especially for patients who need to detect tumors at an early stage. Since patients do not have a specific scanning site, they can only choose to have a wide body scan to catch the fish, which is even more costly and unaffordable for ordinary patients. Is there a relatively economical and non-invasive test that can detect the problem by drawing blood like common cold and fever? The answer is yes. Scientists have found that tumor cells, as the terrorist killers of the healthy organism, have various means to escape the sanction of the body’s immune organs. But the net is wide open, no leakage, and then the cunning fox will also reveal the tail, tumor cells in the evil at the same time, but also inevitably left a trace. This is the tumor marker (Tumor Marker) that scientists have been trying to find. Tumor markers are chemical-like substances that reflect the presence of a tumor. They either do not exist in normal adult tissues but only in embryonic tissues, or the content in tumor tissues greatly exceeds the content in normal tissues. Their existence or quantitative changes can suggest the nature of the tumor, which can be used to understand the tumor’s histogenesis, cellular differentiation, and cellular function, in order to help the diagnosis of the tumor, classification, prognosis, and therapeutic guidance. However, there are many kinds of malignant tumors and different tumor markers for different tumors, so it is unrealistic for patients to have their blood drawn once for each tumor marker. Therefore, scientists fix monoclonal antibodies of various tumor markers on protein chips, which are specially used to capture various tumor marker antigens in the tested serum, so that the value of various tumor markers can be detected by drawing blood once. Common tumor markers include AFP, CEA, NSE, CA19-9, CA242, PSA and other internationally recognized markers related to multiple tumors. Currently, there are 12 markers with more clinical applications, which are commonly known as Carcinoma 12, or C-12 for short. These 12 tumor markers are selected through a large number of scientific experiments and clinical case analysis. These 12 tumor markers are selected after a lot of scientific experiments and clinical cases, and the abnormality of each index has its corresponding practical significance. Some of these markers are like fingerprints left behind by the murderer, which will directly reveal the identity of the murderer once discovered. For example, AFP, i.e. alpha-fetoprotein, when this index rises a lot, we highly suspect that this killer is liver cancer, especially when AFP>500 micrograms per liter, the positive rate of diagnosing liver cancer can reach 70%-90%; another example is PSA, i.e. prostate specific antigen, the positive rate of which reaches more than 60% in prostate cancer, and when we see the abnormality of this index, we have to highly suspect that the possibility of prostate cancer is present. However, not every tumor killer will leave their fingerprints furtively, sometimes the evidence found does not fully show the identity of the killer, so the relationship between tumor markers and tumors is not an absolute one-to-one correspondence. For example, CEA, carcinoembryonic antigen, its elevation is mainly seen in colon cancer, but also seen in pancreatic cancer, breast cancer, lung cancer, thyroid cancer, etc.; and then CA19-9, its elevation is mainly seen in pancreatic cancer, but also can be seen in lung cancer, colon cancer, stomach cancer. Although the elevation of these indicators does not directly lock the murderer, but it also plays an early warning role, which is conducive to the next step of examination, such as imaging tests to clarify the diagnosis. Trial of a criminal often requires human evidence and physical evidence, only one piece of evidence to determine the case will often lead to wrongful convictions, so we can not simply use the C-12 test to confirm the diagnosis of the tumor. For example, the PSA indicator is abnormal, although it is common in prostate cancer, but some patients with prostate hypertrophy and prostate hyperplasia can also be elevated. As the marker test is a reference and comparison, certain tumor markers with relatively poor specificity also exist in normal and embryonic tissues, and the reference range of tumor markers is not absolutely accurate, many tumor markers are mildly elevated and have no practical significance, coupled with the experimental error, we should not judge malignant tumors as soon as we see an elevated test value. We should not judge a malignant tumor at the first sign of elevated test value. We should pay more attention to the elevation and development of the test value than the simple elevation of the value, and should not make a final decision. The test needs to be followed up and reviewed, such as repeating the test in one month, two months and three months, and combined with the medical history, clinical symptoms, signs, and other tests to make a comprehensive judgment, especially through the pathological biopsy examination, and then make a definitive diagnosis. Often patients and friends find that the C-12 test is abnormal in a certain item, then appear pessimistic mood, thinking that the death sentence has been pronounced. In fact, this is not necessary. The right approach for patients is to actively cooperate with doctors for further examination and treatment, maybe the subsequent examination is just a false alarm, even if the tumor is really a tumor, due to early detection, there is even a possibility of cure, which is more worth celebrating, isn’t it? C-12 test is beneficial to the census and screening of tumors, and helps to judge the prognosis and efficacy of tumors. It is believed that with the progress of science and the development of medicine, the detection of tumor markers will continue to benefit mankind in the direction of “broader, wider, and more accurate”, and the invisible killers of malignant tumors will be gone at last.