Abstract: Sound molecular diagnostic techniques are the basis and prerequisite for individualized treatment. The relationship between individualized treatment and efficacy, and prognosis of patients with malignant tumors has received increasing attention. In the research and clinical application of risk assessment, early diagnosis, molecular typing, tumor biological behavior prediction, prognosis assessment, drug screening, and efficacy monitoring of malignant tumors, molecular diagnostic techniques have demonstrated great advantages. The selection of the most appropriate antitumor drugs for different patients through molecular diagnostic techniques has become a necessary path to improve the efficacy, reduce adverse effects, and economic burden in colorectal cancer treatment. Colorectal cancer is a common malignant tumor of the gastrointestinal tract, occupying the second place among gastrointestinal tumors. The prevalent site is rectum and the junction of rectum and sigmoid colon, accounting for 60%. Its incidence rate increases with age, starting from 40 years old and peaking from 60 to 75 years old. The ratio of men to women is 2:1. Colorectal cancer has obvious geographical distribution and family hereditary factors. The incidence rate is higher in North America and Western Europe, and colorectal cancer in the United States is the second cause of all cancer deaths. Data show that colorectal cancer has jumped to the third place in China’s tumor incidence ranking, and with urbanization and population aging, the incidence rate of colorectal cancer in China is expected to continue to rise in the future, and the prevention and control situation of colorectal cancer is very serious. In recent years, as the relationship between individualized treatment and efficacy and prognosis of tumor patients has received widespread attention and importance from clinical oncologists, individualized treatment of colorectal cancer has become an increasingly hot topic, and the prerequisite for individualized treatment is the application of specific molecular diagnostic techniques. At present, molecular diagnostic techniques have been widely used in various aspects of early diagnosis, molecular typing, biological behavior, prognosis prediction, drug screening and efficacy monitoring of malignant tumors, etc. The research on individualized diagnosis and treatment of colorectal cancer is relatively mature, but still needs to be actively explored. Molecular diagnostic technology is to directly monitor disease-related genes and their products, to explore the mechanism of disease occurrence and development at the molecular level, and to provide parameters such as the structure and expression level of genetic material, related epigenetic information, and the structure and expression status of genes involved in the metabolism of anti-tumor drugs in tumor patients, so as to provide key information for disease prevention and diagnosis, efficacy assessment and prognosis judgment. It provides key information and decision basis for disease prevention and diagnosis, efficacy assessment and prognosis judgment. The birth of modern predictive medicine molecular diagnosis can be traced back to 1978. Kan et al [1], a famous Chinese-American scientist, first applied liquid-phase DNA molecular hybridization to successfully perform the genetic diagnosis of sickle cell anemia, which marked the era of molecular genetic diagnosis in clinical testing and diagnosis. With the continuous improvement and maturation of molecular genetic diagnosis technology, the fields and applications of molecular genetic diagnosis have been expanding. In particular, the introduction of polymerase chain reaction (PCR) technology in the mid-1980s and the launch of the Human Genome Project in the early 1990s have further promoted the development of molecular genetic diagnosis technology. With the rapid development of genetic testing technology and genetic analysis tools, molecular diagnostic techniques have been continuously innovated, especially in the diagnosis of genetic and oncological diseases. Currently, the more mature molecular detection technologies include gene microarrays, fluorescent in situ hybridization, RNA blotting, protein microarrays, protein blotting and flow cytometry [2]. To carry out individualized treatment, it is particularly important to explore highly sensitive and specific molecular markers, which are used today for basic and clinical research using molecular diagnostic techniques: 1 markers at the DNA level, gene mutations, single nucleotide polymorphisms, changes in DNA copy number, chromosomal abnormalities, and abnormal methylation; 2 markers at the RNA level, expression of transcription factors and micro-RNA levels; 3 markers and markers at the protein level, growth factors, cell surface receptors, phosphorylation status of proteins, and peptides released into the serum by tumor cells [2]. Monitoring parameters such as gene mutations, mRNA expression levels and genotyping in tumor tissues provides a scientific basis for clinical individualized treatment, improves the efficiency of drug therapy, and reduces the toxic side effects of drugs. Currently, several molecular level testing protocols have been incorporated into clinical guidelines for individualized tumor treatment. The concept and significance of individualized therapy Individualized therapy is based on the information of each patient to develop a treatment plan, usually based on the differences in gene composition or expression changes to assess the therapeutic effect or toxic side effects of patients, and to provide the most appropriate drug therapy for each patient [3]. In the Emperor’s Classic of Internal Medicine, the Chinese medical theory of evidence-based treatment, which is “different treatment for the same disease and different treatment for different diseases”, fully reflects the idea of individualized treatment. The main meaning is to select the appropriate treatment plan for the individual patient, aiming to improve the target of treatment, protect the patient from the delay of treatment time caused by the ineffective use of drugs according to experience and/or guidelines, reduce or avoid the adverse effects of chemotherapeutic drugs on the body, and reduce the psychological and economic burden of the patient to maximize the patient’s In recent years, the individualized treatment for tumor patients has been developed. In recent years, the research and exploration of individualized treatment for tumor patients has become the focus of oncologists, and the perfect molecular diagnostic technology is the foundation and prerequisite for the realization of individualized treatment. Molecular diagnostic techniques in colorectal cancer diagnosis and treatment and research progress 3.1 Prediction of high-risk patients or early diagnosis of colorectal cancer Molecular diagnostic techniques can predict high-risk patients, especially those with family history of tumor, by detecting certain genetic changes; or early detection of patients with insidious early tumor and timely adoption of effective interventions, which can greatly improve the cure rate and reduce the mortality rate. . Current research has found that about 1/4 of the families of colorectal cancer patients have a family history of cancer, half of which are also gastrointestinal tumors. Due to the genetic alteration of normal cells, patients with cancer get a susceptibility from heredity in their bodies, and with some stimulating factors, the tissue cells grow rapidly and develop into cancer, and the cell genetic mutation becomes malignant cells with genetic characteristics of tumor, which shows the familial nature of cancer. 2008, a study was conducted by detecting the instability of microsatellite and MLH1 (49%), MSH2 ( 38%), MSH6 (9%) and PMS2 (2%), screening for Lynch syndrome (hereditary site-specific colorectal cancer) in 500 colon cancer patients showed that the efficiency of these two methods to screen for Lynch syndrome was 100% and 94%, respectively [4]. 2015 National Comprehensive Cancer Network (NCCN ) clinical practice guidelines in oncology recommended the use of this diagnostic technique to screen for Lynch syndrome in patients with newly diagnosed colorectal cancer, and it was estimated that Lynch syndrome could be detected in one case per 35 newly diagnosed colorectal cancer patients. Therefore, the application of specific molecular diagnostic techniques can detect the high-risk group of corresponding tumors or second primary cancers early and give timely and effective interventions, which can greatly reduce the incidence and mortality of cancer. 3.2 Molecular staging of colorectal cancer Compared with the traditional tumor staging based on the morphological characteristics of tumor cells under the microscope, the main difference of molecular diagnostic techniques for tumor staging is that they can analyze the tumor at the molecular level in a more detailed and accurate way, and then evaluate the biological behavior of the tumor and the prognosis of patients more accurately, and ultimately guide the clinical individualized treatment. The TNM staging based on tumor anatomy, which is commonly used in clinical practice, is unable to classify tissue heterogeneity well and thus cannot make accurate judgment on patient prognosis and regression, which makes molecular staging of colon cancer necessary. N. Jewel Samadder et al [5], Department of Gastroenterology, University of Utah Cancer Institute, Salt Lake City, Utah, USA, validated the correlation between clinicopathological characteristics of colorectal cancer patients and molecular staging of colorectal cancer using large samples based on previous studies, and found that the currently proposed molecular staging can play a role in determining TNM staging and survival of colorectal cancer, but also pointed out that in order to validate the above findings still However, it was also pointed out that more clinical data are needed to validate the above conclusions. 3.3 Tumor markers for colorectal The most mature molecular diagnostic techniques used in the diagnosis and treatment of colorectal cancer are the detection of serum CEA and CA199, a glycoprotein produced by colorectal cancer tissues, which can cause immune response in patients as an antigen and can be widely found in gastrointestinal cancers of endodermal origin, but it is not a specific marker for malignant tumors and has only an auxiliary value in diagnosis. In addition, there is a clear relationship between serum CEA level and the stage of colorectal cancer, the more advanced the lesion, the higher the CEA concentration. CA199 is a mucin-type glycoprotein tumor marker, a glycolipid on the cell membrane, named for the recognition by murine monoclonal antibody 116NS19-9, and is the most sensitive marker reported so far for pancreatic cancer, as well as a gastrointestinal tumor present in the blood circulation. CEA combined with CA199 reflects the possibility of tumor presence and is a better tumor marker for judging the efficacy, disease progression, monitoring and prognosis estimation of colorectal cancer, but its specificity is not strong, sensitivity is not high, and its role in early tumor diagnosis is not obvious. With the research exploration of molecular diagnostic technology, a sialylated sphingolipid antigen CA242, which also has a sensitivity of 60%-72% for colorectal cancer, is a relatively new tumor marker applied in clinical practice. 3.4 Used to guide the treatment of colorectal cancer Chemotherapy remains one of the important modalities for the treatment of colorectal cancer. The goal of oncologic chemotherapy is to improve efficacy and reduce toxic reactions through individualized treatment regimens. Due to individual genomic differences and tumor heterogeneity, different individuals with the same clinicopathological features may have different responsiveness to the same chemotherapeutic agent or chemotherapy regimen. For patients with recurrence, the effectiveness of empirical drug use is only 10%-30%. Chemosensitivity assays are laboratory techniques that detect the killing or inhibition of tumor cells by specific chemotherapeutic agents after they have been isolated from the body, and also allow a preliminary assessment of the adverse effects of chemical agents. classification system for molecular typing of colorectal cancer development. They identified three major intrinsic subtypes of colorectal cancer (A, B, and C). Subsequently, 543 stage II or III tumor samples were included to validate the classification system. Of these, 21.5% were subtype A, 62.0% were subtype B, and 16.5% were subtype C. Patients with subtype C tumors tended to have the poorest prognosis and were a class of mesenchymal gene expression phenotypes that received no benefit from adjuvant chemotherapy with fluorouracil (5-FU). Patients with subtypes A or B tumors have a better clinical prognosis, have a higher proliferation and epithelial cell phenotype, and are able to benefit from adjuvant chemotherapy with 5-FU. The subtypes of these are potentially clinically relevant, and the difference between them lies in their biological and clinical outcomes, thus requiring different therapeutic strategies. Cetuximab is a human-mouse chimeric immunoglobulin antibody that binds and inhibits EGFR. another similar agent, panitumumab, is a fully humanized monoclonal antibody that inhibits EGFR. In 2009, the NCCN and the American Society of Clinical Oncology recommended that all patients with advanced metastatic colorectal cancer should be tested for KRAS gene status prior to treatment, and that wild-type KRAS gene as a molecular marker for selecting anti-EGFR-targeted drug therapy [7]. The effective tolerable dose for VEGF, EGFR, mTOR and HER2 pathway inhibitors is also more difficult to clarify at present due to superimposed or unknown toxicity. Only through the clarification of biopredictive markers or mechanisms of resistance to primary and secondary tumor therapy can we select patients most likely to benefit from targeted therapy. Therefore, the detection of effective molecular targets is necessary to achieve individualized treatment for tumor patients, which improves the efficacy and reduces the adverse effects and economic burden brought by blind drug use to patients for whom certain drugs are ineffective. 3.5 Prognosis of colorectal cancer patients Molecular diagnostic techniques to detect markers related to tumor prognosis can predict the prognosis of tumor patients. in a case-control study, Siemens et al [8] divided 94 patients with primary colorectal cancer into experimental (n=47; those with liver metastases, M1) and control groups (n=47; those without distant metastases, M0), and detected miR-34 in the enrolled patients The methylation levels of miR-34a and miR-34b/c promoter CpG islands, and the expression levels of miR-34a and miR-34a targets (c-MET, Snail and β-catenin) in tumor tissues were examined. The results showed that miR-34a methylation (P=0.014), c-MET (P=0.031) and high expression of β-catenin (P=0.058) were positively correlated with the occurrence of distant metastasis in colorectal cancer, and the frequency of these three markers was abnormally high in tumor tissues with distant metastasis. This suggests that simultaneous detection of miR-34a methylation levels, c-MET and β-catenin expression levels can be used as indicators to predict the occurrence of distant metastasis in colorectal cancer patients. 4. Summary With the development of molecular diagnostic technology, great progress has been made regarding the diagnosis and treatment of colorectal cancer, and it has shown great advantages in guiding the individualized treatment of colorectal cancer. In particular, molecular targeted therapy is developing rapidly, but there is still a lot of research needed in the drug resistance mechanism of colorectal cancer treatment. For the diagnosis and treatment of colorectal cancer, we sincerely expect the perfect combination of multiple disciplines.