Cancer is a term with a very high occurrence rate in today’s society and an important factor that affects the happiness and harmony of millions of families, and most people are afraid of talking about cancer. In fact, there are three stages in the development of cancer, including precancerous lesions, in situ cancer and invasive cancer. There are many cancers that can be killed in the cradle if we can pay attention to them during the precancerous stage and treat them. Therefore, we need to understand some general knowledge about precancerous lesions to protect the health of ourselves and our family. In fact, the so-called precancerous lesions refer to certain lesions that may become cancerous if they continue to develop, such as: mucosal leukoplakia, junctional nevus, chronic atrophic gastritis, cervical erosion, multiple adenomatous polyps of colorectum, certain benign tumors, etc. For precancerous lesions, some ambiguous understanding must be clarified: ① Precancerous lesions are not cancer, therefore, they should not be equated with cancer. ②Most precancerous lesions will not turn into cancer, only some of them may turn into cancer. ③ Pre-cancerous lesions should not be expanded to treat some lesions that are not pre-cancerous, such as general skin moles, common peptic ulcers and chronic gastritis as pre-cancerous lesions. Here we briefly introduce several common precancerous lesions. 1.Mucosal leukoplakia histologically refers to white patches occurring on the surface of mucous membrane, and hyperkeratosis of mucosal epithelial surface is one of the characteristics of leukoplakia. As a disease, it mainly refers to those mucosal leukoplakia characterized by hyperkeratosis and epithelial hyperplasia. Dermatopathologists have long viewed mucosal leukoplakia as a pre-cancerous lesion and believed that 20% to 30% would eventually develop into cancer. However, most leukoplakia is now found to be harmless, and only a few can become malignant, with an average incidence of slightly more than 4%. Mucocutaneous leukoplakia in dermatology includes lesions in both the oral cavity and vulva, with vulvar leukoplakia occurring mainly in women, hence the name female leukoplakia. Although the probability of mucocutaneous leukoplakia becoming malignant is low, it is still a disease that will bring some pain or discomfort to patients. How should it be treated? In general, it varies from person to person. First of all, attention should be paid to removing local irritants, such as improving oral hygiene, treating diseased teeth, etc. The female pubic area should be washed frequently to keep it clean, while actively treating systemic diseases. In addition, the decoction of Chinese herbs, Phellodendron, etc. can often receive good results, and the adult medicine Jieer Yin can also play the same role. Generally speaking, leukoplakia with simple causes and milder conditions can often disappear after removing the causes or by simple medication. However, there are cases where drug treatment is ineffective, especially when there are local ulcers, hard nodes or superfluous organisms, and those with pathological tendency to cancer should be surgically removed. In conclusion, the symptoms of leukoplakia vary in severity and duration, from a few months to several years or even a dozen years. There is no one special medicine or special method for all patients. 2. Junctional nevus is a brown or black rash, which can be slightly elevated, 2-8mm, round, with clear border, uniform color, smooth and hairless surface. It can occur in any area. Most of the nevi occurring in the palmoplantar and external genitalia are junctional nevi. Junctional nevus is characterized by the activity of nevus cells at the junction of epidermis and dermis, and has the tendency of malignant transformation, especially the nevus that grows on the palms of hands, soles of feet and other easily stimulated parts should be more alert. Clinically, some nevi and mixed nevi can become malignant melanoma under the stimulation of certain factors. Although junctional nevi and mixed nevi have been proven to have a tendency to become malignant, very few of them actually develop into malignant tumors. At present, it is believed that repeated stimulation such as friction, needle picking, incomplete excision, light, electrocautery, erosion with drugs and one’s own endocrine disorder may be the triggering factors to stimulate the malignant transformation of junctional nevus or mixed nevus into melanoma. When a nevus is malignant, there are often some abnormal manifestations, which should be paid special attention to: ① sudden acceleration of growth and obvious enlargement in a short period of time; ② obvious deepening of color compared with the previous one or uneven color; ③ sudden loss of hair growth; ④ local itching and painful feeling in the nevus; ⑤ moist or crusting on the surface of the nevus; ⑥ erosion, rupture, bleeding and inflammation on the surface of the nevus; ⑦ the edge of the nevus, which was clear, suddenly expands to the (vii) the edge of the mole is clear but suddenly expands to the surrounding area, the edge is irregular and the boundary with normal skin is not clear, or there is redness around the mole; (viii) hard nodules appear in the center of the mole or satellite like scattered tiny pigment spots or nodules appear around the mole. If you find the above signs or suspect malignant tendency, you need to go to hospital for relevant examination as soon as possible. Pathological examination can clarify the diagnosis. In general, the lesion should be removed by excisional surgery, and the whole piece of normal skin and subcutaneous fat of 0.5~lcm around the lesion should be removed for pathological examination. If it is confirmed that there is malignant change, then according to the depth of infiltration, and then decide whether to perform a supplementary extensive excision. 3, chronic atrophic gastritis Histology is atrophy, degeneration, reduction or disappearance of intrinsic glands and corresponding regeneration, hyperplasia and intestinal metaplasia, which may or may not be accompanied by infiltration of inflammatory cells. It is a common gastric disease, accounting for 10% to 30% of chronic gastritis. Arteriosclerosis, inadequate gastric blood flow, and addiction to tobacco, alcohol, and tea can easily impair the barrier function of the gastric mucosa and cause chronic atrophic gastritis. Pathologically, when chronic atrophic gastritis occurs, the gastric mucosa atrophies and is replaced by epithelial cells of the intestine, i.e., intestinal chemosis; inflammation continues to evolve, the cell growth is atypical, i.e., interstitial changes; even cell proliferation and carcinogenesis. The clinical manifestations of chronic atrophic gastritis are only indigestive symptoms such as epigastric fullness, belching, and decreased appetite, sometimes resulting in anemia due to destruction of intragastric factors and malabsorption of vitamin B12. Endoscopy and biopsy are the only means to confirm the diagnosis of chronic atrophic gastritis.