The incidence and mortality of cancer have been increasing alarmingly in China and worldwide[1].Unlike other chronic diseases such as metabolic,cardiovascular,and neuropathies,most cancers,especially metastatic ones,are still essentially uncontrollable in spite of significant progresses such as early diagnosis and immunotherapies.Fortunately,human cancer generally takes about 10-30 years to develop;hence there is a window of opportunity to prevent cancer before it becoming metastatic and radio/chemotherapeutic resistant.Indeed,prevention has made huge contribution to cancer control in the United States and some European countries,and chemoprevention is one of the most attractive strategies[2].