Precancerous lesions are certain benign lesions with cancerous potential, which may turn into cancer if left untreated. However, it does not mean that precancerous lesions will definitely turn into cancer, and not all cancers come from precancerous lesions. Doctors are not fully aware of which diseases are precancerous lesions, but the following are more certain: 1.White patches of mucous membrane: white patches in the oral cavity, esophagus, cervix, vulva, etc. can be transformed into squamous carcinoma, especially in vulva. 2.Atypical hyperplasia of the uterine cervix: that is, the proliferating cells have morphological changes, but the degree of change is less than that of cancer, and there is no essential change yet. This condition mostly occurs in those who have cervical erosion. 3.Cystic hyperplasia of breast: It is mostly seen in women over 40 years old, and the hyperplastic breast tissue is thickened in sheets. 4, colorectal adenoma and adenomatosis: multiple or large adenomas have a high rate of cancer. There is also a kind of familial adenomatosis of the colon, which is a hereditary disease. If not treated or not treated in time, almost 100% of them will develop into cancer. 5. Chronic atrophic gastritis and gastric ulcer: There are many types of gastritis, and one type of gastric mucosa with atrophy-like changes is more likely to become malignant. Although gastric ulcer can become cancerous, but the cancer rate is low. It is generally believed that duodenal ulcers are not cancerous. 6. Chronic skin ulcers or burn scars can also become cancerous.