There is no clear cause for cancer, and there are danger signs of cancer, but no obvious precursors. If a lump appears anywhere on the body and grows in size, this is a red flag to be aware of. It is also important to pay attention to ulcers on the skin that do not heal, as this is also a precursor of cancer. In addition, systemic symptoms mainly include fever and anemia, which require prompt medical attention. In terms of specific sites of cancer, nasopharyngeal cancer may have retractable nosebleeds, skin disease may show rapid growth or ulceration of moles, and attention should be paid to tonsils in the pentatomical department. If only painless masses grow and do not improve after treatment, they should also be treated promptly. If there is unexplained hoarseness that gradually worsens, pay attention to lung cancer or laryngeal cancer. Some patients with swallowing difficulty should pay attention to the possibility of esophageal cancer and need further examination. In addition to the main common cancer aura mentioned above, you should also pay attention to the unexplained weakness and dizziness of the whole body. In the respiratory system, patients with cough or hemoptysis and a history of smoking should pay attention. In the breast, especially in women, if a lump is found, it should be reviewed regularly. Patients with blood in the stool or hemoptysis in the gastrointestinal system should also be diagnosed by gastroscopy. Patients with yellow skin staining in the infection department should pay attention to exclude the possibility of liver cancer.