Precancerous lesions are lesions that are not cancerous in themselves, but are prone to cancer on top of it. What are the common precancerous lesions? 1.Mucosal leukoplakia: Mucosal leukoplakia is the most common precancerous lesion, which usually occurs on the mucosal surface of lips, tongue, esophagus, cervix, vulva, etc. It can also occur on the glans penis or inner plate of foreskin in elderly men. Initially, it is mostly a white smooth soft spot with little sensation when touched by hand. Later, it develops into a white or gray spot that protrudes from the mucosal surface and feels rough to the touch. Finally, ulcers occur on the surface and the base becomes thick and hard, which is a sign of malignant lesions. It should be closely observed and should be treated early. 2.Cervical erosion and ectropion: some information shows that active treatment of cervical erosion is the key measure to prevent cervical cancer. 3.Cystic hyperplasia of breast: also called “fibrocystic mastopathy”, which is characterized by nodules of different sizes in the breast with pressure pain, most of which occur before menopause. Most of them occur before menopause, and if not treated actively, about 20% of them may develop into breast cancer. If there are breast cancer patients in the family, their family members should be examined and treated early. 4. Gastric ulcer: Many gastric cancers are malignant on the basis of gastric ulcer (not duodenal ulcer, which rarely becomes malignant), and some occur on the basis of atrophic and hypertrophic gastritis, which should be noted. Chronic atrophic gastritis, if accompanied by intestinal epithelial metaplasia, mucosal epithelial atypical hyperplasia, may be carcinogenic. Chronic ulcers, scars and fistulas: Especially chronic ulcers on the lower legs, traumatic and chemically damaged ulcers, scars after large burns, scalding and frostbite, long-standing osteomyelitis and tuberculous fistulas, etc., all have the possibility of cancer. In this case, on the one hand, thorough treatment should be done, and on the other hand, hospital examination should be conducted. 6.Ovarian cysts: about half of plasmacytic cystic adenomas evolve into cancer, and about 1/3 of mucinous cystic tumors evolve into cancer. 7.Chronic hepatitis B, hepatitis C and cirrhosis: if left untreated for a long time, they may deteriorate into cirrhosis and liver cancer. 8.Circumcision and prepuce: 80%-100% of penile cancer is accompanied by circumcision and prepuce. 9.Polyps of cervix, rectum, colon and stomach: they are also common precancerous lesions. Polyps often cause bleeding and have health effects, so they should be treated early. Especially adenomatous polyps have a tendency to become malignant and have a family history. 10.Burn scar: with keratotic hyperplasia or ulcers that do not heal for a long time, it can evolve into squamous cell carcinoma. 11.Colored nevus: rapid increase in size, dark color, hair loss or satellite like care around the nevus within a short time, local itching and pain, etc., may be the precursor of malignant transformation. 12.Chronic dystrophic dermatitis, keratosis, warts, papilloma: sometimes they can also become malignant, especially in the parts that are vulnerable to friction, special attention should be paid to them, and they must be treated or removed early. 13. Testicular tumors are likely to occur on the basis of cryptorchidism (testicles in the abdominal cavity) or incomplete testicular descent, so it is best to perform surgery early. 14.Atypical hyperplasia of many parts such as esophageal mucosa and skin has the possibility of transition to cancer, and those who have these lesions should be reviewed regularly.