cancer - Prevention
Cancer prevention is defined as active measures to decrease the incidence of cancer. This can be accomplished by avoiding carcinogens or altering their metabolism, pursuing a lifestyle or diet that modifies cancer-causing factors and/or medical intervention (chemoprevention, treatment of pre-malignant lesions). The epidemiological concept of "prevention" is usually defined as either primary prevention, for people who have not been diagnosed with a particular disease, or secondary prevention, aimed at reducing recurrence or complications of a previously diagnosed illness.

Observational epidemiological studies that show associations between risk factors and specific cancers mostly serve to generate hypotheses about potential interventions that could reduce cancer incidence or morbidity. Randomized controlled trials then test whether hypotheses generated by epidemiological trials and laboratory research actually result in reduced cancer incidence and mortality. In many cases, findings from observational epidemiological studies are not confirmed by randomized controlled trials.

• • cancer - Prevention - Modifiable ("lifestyle") risk factors
    • Examples of modifiable cancer risk factors include alcohol consumption (associated with increased risk of oral, esophageal, breast, and other cancers), smoking (although 20% of women with lung cancer have never smoked, versus 10% of men), physical inactivity (associated with increased risk of colon, breast, and possibly other cancers), and being overweight (associated with colon, breast, endometrial, and possibly other cancers). Based on epidemiologic evidence, it is now thought that avoiding excessive alcohol consumption may contribute to reductions in risk of certain cancers; however, compared with tobacco exposure, the magnitude of effect is modest or small and the strength of evidence is often weaker. Other lifestyle and environmental factors known to affect cancer risk (either beneficially or detrimentally) include certain sexually transmitted diseases, the use of exogenous hormones, exposure to ionizing radiation and ultraviolet radiation, and certain occupational and chemical exposures.
  • cancer - Prevention - Diet
    • The consensus on diet and cancer is that obesity increases the risk of developing cancer. Particular dietary practices often explain differences in cancer incidence in different countries (e.g. gastric cancer is more common in Japan, while colon cancer is more common in the United States). Studies have shown that immigrants develop the risk of their new country, often within one generation, suggesting a substantial link between diet and cancer. Whether reductions obesity in a population also reduces cancer incidence is unknown.
  • cancer - Prevention - Chemoprevention
    • The concept that medications could be used to prevent cancer is an attractive one, and many high-quality clinical trials support the use of such chemoprevention in defined circumstances.