Depending on the location of lesions, common precancerous lesions include: 1) Mucous membrane (1) Mucous membrane leukoplakia, which often occurs in the mucous membrane of oral cavity, esophagus, vulva and cervix, with pathological changes of excessive proliferation and keratinization of squamous epithelium. (2) Pigmented nevus in the area susceptible to abrasion. (3) Aged skin keratosis. (4) Pigmented dry dermatosis. (5) Chronic ulcers of the skin and long-standing sinus tracts may induce carcinogenesis due to the proliferation of squamous epithelium caused by long-term chronic stimulation. Breast (1) Cystic hyperplasia of breast (mastopathy), caused by endocrine disorders, mainly manifests as nodules of masses of variable size, medium texture and poorly defined borders that can be felt in the breast, which can be pushed, sometimes accompanied by periodic pain related to menstruation, and pathology with intraductal papillary hyperplasia is prone to carcinogenesis. (2) Intraductal papilloma of the breast, with the possibility of malignant transformation in about 6-8% of cases. (3) Fibroadenoma, often a single, hard, smooth, well-defined, easily pushed mass, also has the potential for malignant transformation. 3, digestive system (1) chronic atrophic gastritis and gastric ulcer. (2) Colon and rectal polyps, especially those with family history and multiple occurrence, have a higher possibility of cancer. (3) Chronic viral hepatitis B and liver cirrhosis. 4, reproductive system (1) prepuce, prepuce. (2) Cervical erosion, which can cause epithelial regeneration and repeatedly lead to atypical proliferation of squamous epithelium and further development of cervical cancer. (3) Staphyloma can develop into chorioepithelial carcinoma. (4) Cryptorchidism. 5. Other parts Benign tumors in some parts of the body may turn into cancer under the effect of certain factors.