It is impossible to generalize how far precancerous lesions are from cancer. It may be as short as a few months, or as long as a year or two or more, and with timely intervention, it may not become cancerous. Pre-cancerous lesions refer to lesions that have the potential to develop into cancer. Such lesions do not necessarily become cancerous, and in general, some pre-cancerous lesions will not develop into cancer if the patient is able to actively intervene in the treatment. However, if left untreated, they may eventually become cancerous. Due to the different progress of the disease and individual differences, the time before they become cancerous cannot be determined. Chronic atrophic gastritis, junctional nevus, mucous membrane leukoplakia, certain benign tumors, multiple adenomatous polyps of the colorectum and other diseases may lead to cancer. In order to reduce the chances of cancerous lesions, patients should participate in regular medical checkups, and follow the instructions of the doctor for active treatment once discomfort exists.