Malignant tumors are caused by multiple carcinogenic factors undergoing several stages. The occurrence and development of tumors may be prevented and blocked if some effective interference factors are brought into play.1 At present, there are two main subjects for the researches, that is, blocking the precancerous lesions and blocking the develop-ment of tumors. The former focuses on the removing of carcinogenic factors and on the chemoprophylaxis of cancer, while the latter on the inhibition of cancer cell infiltration and cancerometastasis. These are summarized as follows.