Talking about cancer is scary! On the list of common cancers, the incidence of colorectal cancer has jumped to the 3rd to 5th place, becoming the “dark horse” of the cancer world. Some colorectal cancers can be hereditary! Colorectal cancer is no longer a matter for the elderly, it can be found in the age of 20, 30 and 40! Mr. Lynch syndrome is an autosomal dominant disorder caused by a germline mutation in the mismatch repair gene (MMR). This “Mr. Lynch” is an acute and abominable guy, what does this mean? (1) Early age of onset, median age is about 44 years, and the time required to develop from adenoma to adenocarcinoma is relatively short, from adenoma to adenocarcinoma in normal people takes 8-10 years, while in patients with Lynch syndrome it only takes 2-3 years; (2) Proximal colon is common, about 70% are located in the proximal side of the splenic flexure; (3) Multiple primary colorectal cancers are significantly increased; (4) High incidence of extraintestinal malignancies, simultaneous and heterochronic multiple primary cancers such as endometrial cancer, ovarian cancer, gastric cancer, intrahepatic cholangiocarcinoma, urological tumors and skin cancer are significantly higher than the normal population – many tumors have to be involved, which is abominable enough; (5) hypofractionated adenocarcinoma and mucinous adenocarcinoma are common and accompanied by lymphocytic infiltration or aggregation of lymph-like cells; (6) vertical inheritance and family aggregation –(6) vertical inheritance and familial aggregation; (7) native manifestation; (8) mostly swelling growth rather than infiltrative growth. The prognosis is better – this is somewhat conscientious and not driven to extinction. Familial adenomatous polyposis (FAP), a veritable FAP, is an autosomal dominant disease caused by an APC mutation. The greatest skill of this veritable “polyp” member is to grow polyps everywhere to identify himself. Those who are intensely phobic may be frightened by him – the intestinal tract is filled with polyps, ranging from tens to hundreds or even thousands. Common symptoms include diarrhea, abdominal pain, and blood in the stool. Patients often suffer from anemia and weight loss due to prolonged exertion during the tug-of-war. The seriousness of the disease lies in the high rate of carcinoma, which is often not limited to one location but is “multicentric”. Adenomatous polyps can appear at the age of 12 or 13, and by the age of 20 the polyps have spread throughout the large intestine. MUTYH-associated polyposis (MAP) is an autosomal recessive disorder caused by mutations in the MUTYH gene, which is very similar to familial adenomatous polyposis. But when this guy shows his fangs, the victims are more at risk – patients with MUTYH mutations have a significantly higher risk of colorectal cancer. Other members of Gardner syndrome (GS) are a rare autosomal dominant disorder characterized by three major features: colorectal polyposis combined with multiple osteomas and soft tissue tumors. Glioma polyposis syndrome is a clinically rare clinical subtype of FAP characterized by familial multiple colonic adenomas with central nervous system malignancies. Polyposis nigricans polyposis nigricans (PJS) is associated with mutations in the SKT11 gene. The three main clinical features are skin mucosal discoloration, gastrointestinal misshapen polyps and familial inheritance. Typical cutaneous mucosal dark spots and/or intussusception, intestinal obstruction or bleeding may occur during childhood. The risk of polyp malignancy increases with age. Polyps can appear throughout the intestinal tract. However, polyps do not stay in the intestine, they can also appear outside the intestine, such as in the bladder and respiratory tract. Familial juvenile colonic polyposis (FJIPC) is autosomal dominant and is mainly associated with mutations in the SMAD4 or BMPR1A genes. FJIPC also has the “virtue” of being “cancer-friendly” in that it can significantly increase the risk of colorectal, small bowel, gastric and pancreatic cancer. Some patients with familial juvenile colonic polyposis may have congenital disorders such as pestle and mortar finger (toe), hypertrophic pulmonary osteoarthropathy, hydrocephalus, cleft lip, cleft palate, congenital heart disease, etc. Carriers of SMAD4 mutation sometimes develop genetically associated capillary hemorrhage, which manifests as recurrent rhinorrhea, dilated skin mucosa or lung capillaries, and arteriovenous malformations of the brain or liver. PTEN malformation syndrome (PHTS) is an autosomal dominant disorder caused by mutations in the PTEN gene and includes Cowden syndrome and BRRS syndrome. cowden syndrome presents with multiple colorectal malformation polyposis, facial papules, acromegaly and oral mucosal papillomas. BRRS syndrome is also an autosomal dominant disorder caused by PTEN mutations and is characterized by colorectal polyposis, macrosomia, lipomatosis, angiomatosis, and genital discoloration. How to prevent hereditary colorectal cancer three early: early detection, early diagnosis and early treatment.