Ways to Prevent Cancer
Prevention is defined as the reduction of cancer mortality via reduction in the incidence of cancer. This can be accomplished by avoiding a carcinogen or altering its metabolism; pursuing lifestyle or dietary practices that modify cancer-causing factors or genetic predispositions; and/or medical intervention (chemoprevention) to successfully treat preneoplastic lesions.
Much of the promise for cancer prevention comes from observational epidemiologic studies that show associations between modifiable life style factors or environmental exposures and specific cancers.
Evidence is now emerging from randomized controlled trials designed to test whether interventions suggested by the epidemiologic studies, as well as leads based on laboratory research, result in reduced cancer incidence and mortality.
Additional examples of modifiable cancer risk factors include alcohol consumption (associated with increased risk of oral, esophageal, breast, and other cancers), 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, being physically active, and maintaining recommended body weight, may all 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 sexual and reproductive practices, the use of exogenous estrogens, exposure to ionizing radiation and ultraviolet radiation, certain occupational and chemical exposures, and infectious agents.
Food and nutrient intake have been examined in relation to many types of cancer. Fruit and vegetable consumption have generally been found in epidemiologic studies to be associated with reduced risk for a number of different cancers; however, it is not currently known which specific components of fruits and vegetables are responsible for the observed associations or if healthy diets are simply associated with other beneficial interventions, e.g., exercise.
Contrary to expectation, randomized trials found no benefit of beta-carotene supplementation in reducing lung cancer incidence and mortality; risk of lung cancer was statistically significantly increased in smokers in the beta-carotene arms of 2 of the trials.
Similarly, randomized controlled trials have found no reduction in risk of subsequent adenomatous polyps of the colon in individuals who have had polyps resected taking dietary fiber supplements compared with those receiving much lower amounts of supplemental wheat bran fiber.
On the other hand, there is evidence from at least 1 randomized controlled trial that calcium supplementation does modestly reduce risk of adenoma recurrence. The “chemoprevention database” gives results of all published randomized controlled trials.
Consumption of red meat and inadequate folic acid intake have also been associated with increased risk of colon cancer.
A large randomized trial is currently underway to investigate whether men taking daily selenium or vitamin E or both experience a reduced incidence of prostate cancer in comparison to men taking placebo pills.
Daily use of tamoxifen, a selective estrogen receptor modulator, for up to 5 years, has been demonstrated to reduce the risk of developing breast cancer in high-risk women by about 50%.
Cis-retinoic acid also has been shown to reduce risk of second primary tumors among patients with primary cancers of the head and neck.
Finasteride, an alpha-reductase inhibitor, has been shown to lower the risk of prostate cancer.
Other examples of drugs that show promise for chemoprevention include COX-2 inhibitors (which inhibit the cyclooxygenase enzymes involved in the synthesis of proinflammatory prostaglandins).
Considerable research effort is now devoted to the development of vaccines to prevent infection by oncogenic agents, and to potential venues for gene therapy for individuals with genetic mutations or polymorphisms that put them at high risk of cancer.
Meanwhile, genetic testing for high-risk individuals, with enhanced surveillance or prophylactic surgery for those who test positive, is already available for certain types of cancer, including breast and colon cancers.