Chemoprophylaxis in gastrointestinal tumors.

Chemoprevention of gastrointestinal tumors uses natural or synthetic agents to arrest, retard or reverse the carcinogenesis process. The prospect of prevention is clearly appealing, especially for colorectal cancer (CRC), that represents the second most common cause of cancer-related death in the Western world. Aspirin is the best studied chemopreventive agent for CRC, with randomized trials demonstrating its efficacy in reducing recurrence of colorectal adenomas in higher risk patients. Optimal chemoprevention requires long-term use and high dose of aspirin that may increase the risk of gastrointestinal bleeding. Other nonsteroidal anti-inflammatory drugs and selective cyclooxygenase-2 inhibitors also reduce the incidence of colonic adenomas, but they are associated with gastrointestinal harms and important cardiovascular events, respectively. Furthermore, cumulative epidemiological and observational data suggest the potential role of hormones as a chemoprotective agent for CRC. The usefulness of folic acid, calcium, and vitamin D awaits further evaluation. Interestingly, combining different agents may maximize effectiveness while limiting drug toxicity. Although many agents have shown positive results in the field of chemoprevention, it cannot yet be accepted as standard medical practice for CRC. In the present review we discuss the most promising agents in CRC chemoprevention, together with their potential mechanisms of action in tumor inhibition.