Human cancer chemoprevention: hurdles and challenges.
Cancer is considered a disease of aging since the risk for developing the disease considerably increases with age. It is estimated that 77% of all cancers are diagnosed in people who fall within the age group of 55 or older. Also, it takes several years from initiation to the development of detectable cancer. One advantage of the long latency is that it provides numerous opportunities for intervention. While intervention approaches cannot be geared towards a whole population, they can nevertheless be directed towards a defined group of people who have a greater relative risk for developing the disease. The idea of cancer prevention through the use of nontoxic agents, preferably from dietary sources, has therefore emerged as an appropriate strategy for controlling the disease. An important aspect of chemoprevention is that agents can be designed for intervention at any stage during the multistage process of carcinogenesis. This process of slowing the progression of cancer is applicable to many cancers with long latency, including prostate cancer. Over the past two decades we have put considerable effort into identifying dietary substances in the form of extracts and pure compounds that can be used for the prevention of prostate and other cancers. Although cancer chemoprevention has proven to be a successful strategy in animals and, to some extent, we can say that the mission has been accomplished, its application to humans has met with limited success. This chapter will discuss various challenges associated with chemoprevention of cancer with the focus on studies with green tea and prostate cancer.