ABSTRACT
Cancer accounts for more than 12% of deaths globally. It is a silent disease characterized by unscheduled and uncontrolled cell proliferation. Almost any mammalian cell can succumb to oncogenic transformation. Majority of human cancers are caused, mediated, or modi ed by environmental factors. Causative agent(s)/factor(s) may also act simultaneously or in sequence to initiate or promote carcinogenesis that often has a long latency period of 20 years or more. Although dose and duration of exposure to exogenous/endogenous carcinogen(s) is one of the determining factors, that alone is not suf cient to explain the exposure-related outcome, as majority of cancers result from complex interactions between environmental exposure(s) and genetic/acquired susceptibility or protective host factors. Epidemiological studies have successfully demonstrated that certain well-de ned exposures (e.g., tobacco, alcohol, ionizing radiation, occupational carcinogens, viruses, etc.) increase the risk of cancers at speci c sites. Causal relationships have been established for some cancers, for example, tobacco use and oral/lung cancer. However, for other cancers (breast, colon, stomach, prostate, esophagus) causative factor(s) still need to be determined. Elimination of known and established carcinogens from the environment, that is, primary prevention of cancer has proven to be rather dif cult due to social, economic, and political reasons (e.g., tobacco). Moreover, despite the tremendous advancement in understanding molecular and cellular basis of cancer and in current treatment modalities including surgery, radiation and chemotherapy, the mortality rates (age-adjusted) for cancer have not declined in the past 50 years.
