There are very many types of cancer, and the time it may take to develop varies from site to site or from stage to stage. Some types of cancer may take a long time to form, such as at least five or six years, or more than ten or twenty years. For example, it may take a long time to develop from precancerous lesions in the stomach to gastric cancer, but some malignant tumors may develop faster, such as small cell lung cancer, which is more malignant, and it may take only about half a year or a few months to develop to brain metastasis from the beginning of the lesion to the later stage. Therefore, cancer must be detected and treated early for better results. Regular health checkups, sometimes together with tumor index examinations, chest and abdominal CT, gastroscopy and colonoscopy, can help detect early cancers.