Prevention

Cancer prevention is defined as active measures to decrease the risk of cancer.^[39] The vast majority of cancer risk factors are due to environmental (including lifestyle) factors, and many of these factors are controllable. Thus, cancer is largely considered a preventable disease.^[40] Greater than 30% of cancer is considered preventable by avoiding risk factors including:tobacco, overweight / obesity, an insufficient diet, physical inactivity, alcohol, sexually transmitted infections, and air pollution.^[41] Not all environmental causes can be prevented. For example, exposure to naturally occurring background radiation cannot be prevented.

Dietary

Main article: Diet and cancer

Dietary recommendations to reduce the risk of developing cancer, including: (1) reducing intake of foods and drinks that promote weight gain, namely energy-dense foods and sugary drinks, (2) eating mostly foods of plant origin, (3) limiting intake of red meat and avoiding processed meat, (4) limiting consumption of alcoholic beverages, and (5) reducing intake of salt and avoiding mouldy cereals (grains) or pulses (legumes).^[42][43]

Proposed dietary interventions for cancer risk reduction generally gain support from epidemiological association studies. Examples of such studies include reports that reduced meat consumption is associated with decreased risk of colon cancer,^[44] and reports that consumption of coffee is associated with a reduced risk of liver cancer.^[45] Studies have linked consumption of grilled meat to an increased risk of stomach cancer,^[46] colon cancer,^[47] breast cancer,^[48] and pancreatic cancer,^[49] a phenomenon which could be due to the presence of carcinogens in foods cooked at high temperatures.^[50] Whether reducing obesity in a population also reduces cancer incidence is unknown. Some studies have found that consuming lots of fruits and vegetables has little if any effect on preventing cancer.^[51] A 2005 secondary prevention study showed that consumption of a plant-based diet and lifestyle changes resulted in a reduction in cancer markers in a group of men with prostate cancer who were using no conventional treatments at the time.^[52] These results were amplified by a 2006 study. Over 2,400 women were studied, half randomly assigned to a normal diet, the other half assigned to a diet containing less than 20% calories from fat. The women on the low fat diet were found to have a markedly lower risk of breast cancer recurrence, in the interim report of December, 2006.^[53]

Medication

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. Aspirin has been found to reduce the risk of death from cancer.^[54] Daily use of tamoxifen or raloxifene has been demonstrated to reduce the risk of developing breast cancer in high-risk women by about 50%.^[55]Finasteride has been shown to lower the risk of prostate cancer, though it seems to mostly prevent low-grade tumors.^[56] The effect of COX-2 inhibitors such as rofecoxib and celecoxib upon the risk of colon polyps have been studied in familial adenomatous polyposis patients^[57] and in the general population.^[58][59] In both groups, there were significant reductions in colon polyp incidence, but this came at the price of increased cardiovascular toxicity.

Vitamins have not been found to be effective at preventing cancer,^[60] although low levels of vitamin D are correlated with increased cancer risk.^[61][62] Whether this relationship is causal and vitamin D supplementation is protective is yet to be determined.^[63] Beta-carotene supplementation has been found to increase slightly, but not significantly, risks of lung cancer.^[64]Folic acid supplementation has not been found effective in preventing colon cancer and may increase colon polyps.^[65]

Vaccination

Vaccines have been developed that prevent some infection by some viruses that are associated with cancer, and therapeutic vaccines are in development^[when?] to stimulate an immune response against cancer-specific epitopes.^[66] Human papillomavirus vaccine (Gardasil and Cervarix) decreases the risk of developing cervical cancer.^[66] The hepatitis B vaccine prevents infection with hepatitis B virus and thus decreases the risk of liver cancer.^[66]

Advances in cancer research have made a vaccine designed to prevent cancers available. In 2006, the U.S. Food and Drug Administration (FDA) approved a human papilloma virusvaccine, called Gardasil. The vaccine protects against 6,11,16,18 strains of HPV, which together cause 70% of cervical cancers and 90% of genital warts. It also lists vaginal and vulvar cancers as being protected. In March 2007, the US Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) officially recommended that females aged 11–12 receive the vaccine, and indicated that females as young as age 9 and as old as age 26 are also candidates for immunization. There is a second vaccine fromCervarix which protects against the more dangerous HPV 16,18 strains only. In 2009, Gardasil was approved for protection against genital warts. In 2010, the Gardasil vaccine was approved for protection against anal cancer for males and reviewers stated there was no anatomical, histological or physiological anal differences between the genders so females would also be protected.