الفهرس 
Introduction and Aim of the workOnly 14 pages are availabe for public view
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Abstract
Although major advances have been made in early detection and treatment, Cancer continues to be a principal cause of morbidity and the second leading cause of mortality in the United States. Solid tumors pose a significant public health problem, specially the ”big four”: prostate, breast, lung and colorectal carcinoma, which represent 57% of newly diagnosed cases of cancer and nearly halfof the deaths from the disease. The grim facts point out the need for a radical change in our approach to treatment of cancers. Chemoprevention is a promising new strategy for reducing the morbidity and mortality associated with cancers. Chemoprevention refers to the use of specific natural or synthetic chemical agents to reverse, suppress or prevent the progression 0 invasive cancer. The ideal chemopreventive agent is safe and non toxic over the long term. It should be easy to take and demonstrated to be effective in randomized trials in humans. The rationals for chemopevention derives from the long-term, multistep nature of carcinogenesis. The changes of a normal cell into a cancerous tumor encompasses three broad, successive stages, initiation, promotion and progressron. Intervention within the multistep carcinogenesis process, is the essences of chemoprevemtion. Approximately 2000 natural and synthetic agents have been shown in experimental system to have chemopreventive activity. Agents that have been studied in tocoperol, selenium, tamoxifen, finasteride, and non steroidal antiinfmmatory drug.