There are many physical, chemical and biological carcinogens in the environment where people live, which can induce tumors under certain conditions. However, although people are exposed to various carcinogenic factors, not all of them develop tumors, which indicates that there is also individual susceptibility, which depends to a large extent on the structural or functional state of genetic material – genes. It is believed that tumor is a genetic disease, because genes (genetic material) and genetic abnormalities play an important role in its development. There are three ways of tumor inheritance: hereditary familial tumor syndrome (single gene inheritance) polygenic tumor genetic susceptibility local tumor cell genetic alteration (acquired) i. hereditary familial tumor syndrome (cancer family cancer family) (incidence about 20%) genetic alteration occurs at the beginning of life germline genetic alteration whole body cells are defective. The genes are located at 5q21, and the gene is located at 5q22. The gene is now located at 5q21. 2. type I neurofibromatosis (NF1) A small number of patients have tumors with a tendency to become malignant. A tumor suppressor gene is known to be closely related to the occurrence of NF1 – NF1 gene, which is located at 17q11.2, and has been isolated and cloned. There are also some tumors that are both inherited and disseminated: 1. retinoblastoma; 2. neuroblastoma; 3. Wilms tumor-renoblastoma) hereditary familial tumor syndrome sporadic familial aggregation more than 3 tumors in 2 generations no aggregation age of onset earlier ≤45 years later >45 years same germ layer manifestation often with or without double organ bilateral onset side onset single organ often Multiple locus occurrence Frequently single locus occurrence Other defects associated with the causative gene Frequently no genetic lesion Occurs in the germ line Only tumor cells (somatic cells) occur. Some hereditary tumors are transmitted in the classical Mendelian manner, but in more cases, only the susceptibility of the tumor is inherited, i.e. predisposing genes. These “susceptibility genes” are predisposing genes. These “predisposing genes” and how they function are not well understood. Many common tumors (e.g., breast, intestinal, gastric, etc.) are usually disseminated, but some patients have a significant family history. In addition, the incidence rate among first-degree relatives of patients is usually 3-4 times higher than in the general population. The mode of inheritance of this type of cancer, although not well understood, suggests the phenomenon of familial aggregation of some tumors or an increased susceptibility of family members to these tumors. Characteristics: a. Showing the interplay of environment and genetics. b. It is not the disease itself that is passed from one generation to the next. c. A complex process of multiple genes. d. The genetic alterations are minor and dominated by SNPs. e. There is slight familial aggregation and high prevalence in specific populations (e.g., 12-25% of colon cancer patients have a family history of bowel cancer). Possible scope of susceptibility gene screening: 1. Chemical substance metabolizing enzyme system. 2.DNA damage repair enzyme system. 3.Immune recognition, regulation and response system. 4.Interaction factors of biological factors in cells. 5. Apoptosis genes. Steps to identify susceptibility genes: 1.Qualification and proposal ofcandidates. 2.SNP discovery and analysis. 3.Frequency test of specific SNPs in high prevalence population. 4.Validation of functional study of genes, relationship between specific SNPs and disease susceptibility. Strategy and methods of the study: 1. Susceptibility genes can only be screened in known genes. 2.The scope of screening is based on the understanding of the etiology and cancer mechanism (multi-level and multi-gene). 3.The experimental and control groups should be set up scientifically and strictly. 4.The main methods are PCR-SSCP, DHPLC, sequencing, gene chips, etc. 5.To combine epidemiological correlation analysis with functional validation in the experimental laboratory. The significance of identifying susceptibility genes: 1. Forecasting of high-risk groups. 2.Intervention and prevention. 3.Early diagnosis and early treatment. 4.Theoretical research issues on the steps and mechanisms of carcinogenesis.