Prevention Snapshot

Overwhelming evidence shows that over half of all cancers – and up to three quarters of some specific cancers – could be avoided by a combination of healthy lifestyle and regular screening (Figure 1) (1-3). Reviewed here are behaviors that studies have found to be established or probable means of lowering cancer risk. Behaviors with less scientific backing are not included.

Whenever possible, the link between duration of a behavior (say, amount of time since quitting smoking) and cancer has been included. However, for a number of behaviors it’s difficult and often impossible to classify exactly when a behavior started and how long it takes to affect risk.

Figure 1 - Source: Wolin et al, 2010 (click figure to enlarge)

Smoking Cessation
Smoking cessation is a touchstone example of a healthy behavior resulting in lower cancer risk. Long term cohort studies have repeatedly shown that the risk of developing lung cancer drops quickly in the years following a person’s last cigarette. After five years, risk is cut in half. After fifteen to twenty years, the risk of lung cancer drops to that of someone who’s never smoked (Figure 2).

Figure 2 - Data source: Speizer et al, 1999 (3) (click figure to enlarge)
Weight Loss 
Overweight and obesity has long been established as a risk factor for cancer. A new report by the American Institute for Cancer Risk says that excess weight causes at least 100,000 cases of cancer each year in the United States (5). A long-running American Cancer Society study in one million men and women found that 14 – 20 percent of all cancer deaths were caused by overweight and obesity (6). And a 2008 combined analysis of studies looking at weight and cancer risk – and which included 2.5 to 5 million people with follow-up ranging from 9 to 14 years – found that a 5 point increase in body mass index significantly increased the risk of at least 13 different cancers (Figure 3) (7).

Figure 3 – Data Source, Renehan et al, 2008 (7) (click figure to enlarge)
Less well established is that weight loss can actually lower cancer risk. This is largely due to the fact that people have a very difficult time losing weight and then maintaining the loss over time, which means most research studies haven’t had enough data over a long enough period to reveal any possible benefits for direct cancer endpoints. However, there is substantial evidence that weight loss has beneficial effects on biomarkers that serve as intermediate endpoints in the pathway to cancer. Lower BMI has been shown, for example, to improve insulin levels (thought to be a causal pathway in colon cancer) and lower blood estrogen levels, an established protective factor for breast cancer (8).

For direct evidence, one good example of the cancer prevention benefits of weight loss comes from a 28 year follow up in the Nurses’ Health Study, which showed that sustained weight loss could cut the risk of postmenopausal breast cancer by over half (Figure 4) (9).

Figure 4 - Data source: Eliassen et al, 2006 (9) (click figure to enlarge)
Physical Activity
Worldwide, lack of physical activity causes nearly two million deaths each year by increasing the risk of most major chronic diseases, including diabetes, heart disease, and a number of cancers. Good data show that increasing physical activity can lower risk of these diseases.

Looking at cancer specifically, long-term observational studies have shown that regular physical activity can substantially lower the risk of both colon and breast cancer by about 20 – 25 percent (figures 5 – 6) (10, 11). 

Figure 5 - Data source: Wolin et al, 2009 (10) (click figure to enlarge)
Figure 6 - Data source: Wolin et al, 2009 (11) (click figure to enlarge)
At least ten infectious agents are known to increase the risk of cancer (Figure 7), and several of them are quite common. Yet, in most instances, only a small proportion of those infected actually go on to develop cancer because it takes a unique set of factors along with the infection to turn normal cells cancerous.

Still, these infectious agents have a substantial impact on cancer worldwide. Of particular importance are human papillomavirus (HPV), which causes cervical cancer; hepatitis B and C viruses, which cause liver cancer; and Helicobacter pylori, which causes stomach cancer.

Good evidence now shows that vaccines can make great progress in preventing many of these infection-associated cancers. One long term study of hepatitis B vaccination found that vaccinated youth had a nearly 70 percent lower risk of developing liver cancer than those who were not vaccinated (Figure 8). 

There are also very promising data on the effectiveness of the new HPV vaccine in preventing cervical cancer (Figure 9) . Because the vaccine has been in use for just a short time, data are only available on the development of cervical pre-cancerous lesions, but studies to date have shown it to be extremely effective in preventing advanced cervical neoplasia, which can frequently advance to invasive cervical cancer if untreated.

Hepatitis B Vaccine

Figure 8 - Data source: Chang et al, 2009 (14) (click figure to enlarge)

Human Papillomavirus (HPV) Vaccine

Figure 9 - Data source: The GlaxoSmithKline Vaccine HPV-007 Study Group, 2009 (15) (click figure to enlarge)
There is strong evidence that certain medications can lower the risk of specific cancers: birth control pills (oral contraceptives) and ovarian cancer; aspirin and colon cancer; and tamoxifen/raloxifene and breast cancer. While medications always have a balance of risks and benefits and are only meant for certain populations of people, these well studied links – specifically between tamoxifen and raloxifene and breast cancer – demonstrate how malleable the risk of cancer can be (Figures 10 – 13).


Figure 10 - Data source: Flossman et al, 2007 (16) (click figure to enlarge)
Tamoxifen and Raloxifene

Figure 11 - Data Source: Cuzick et al, 2007 (17) (click figure to enlarge)

Figure 12 - Data Source: Martino et al, 2004 (18) (click figure to enlarge)

Birth Control Pills (Oral Contraceptives)

Figure 13 - Data source: Beral et al, 2008 (19) (click figure to enlarge)

 Literature Cited
1.         Harvard Report on Cancer Prevention. Volume 1: Causes of human cancer, summary. Cancer Causes Control, 1996. 7 Suppl 1(3): p. S55-58.
2.         Harvard Report on Cancer Prevention. Volume 2: Prevention of human cancer. Cancer Causes Control, 1997. 8 Suppl 1: p. S1-50.
3.         Doll, R. and R. Peto, The causes of cancer:  quantitative estimates of avoidable risks of cancer in the United States today. J Natl Cancer Inst, 1981. 66: p. 1191-1308.
4.         Speizer, F.E., et al., Prospective study of smoking, antioxidant intake, and lung cancer in middle-aged women (USA). Cancer Causes Control, 1999. 10(5): p. 475-82.
5.         American Institute for Cancer Research (2009) New Estimate: Excess Body Fat Alone Causes Over 100,000 Cancers in US Each Year.
6.         Calle, E.E., et al., Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med, 2003. 348(17): p. 1625-38.
7.         Renehan, A.G., et al., Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet, 2008. 371(9612): p. 569-78.
8.         McTiernan, A., et al., Adiposity and sex hormones in postmenopausal breast cancer survivors. J Clin Oncol, 2003. 21(10): p. 1961-6.
9.         Eliassen, A.H., et al., Adult weight change and risk of postmenopausal breast cancer. JAMA, 2006. 296(2): p. 193-201.
10.       Maruti, S.S., et al., A prospective study of age-specific physical activity and premenopausal breast cancer. J Natl Cancer Inst, 2008. 100(10): p. 728-37.
11.       Wolin, K.Y., et al., Physical activity and colon cancer prevention: a meta-analysis. Br J Cancer, 2009. 100(4): p. 611-6.
12.       Bernstein, L., et al., Lifetime recreational exercise activity and breast cancer risk among black women and white women. J Natl Cancer Inst, 2005. 97(22): p. 1671-9.
13.       Franceschi, S., Strategies to reduce the risk of virus-related cancers. Ann Oncol, 2000. 11(9): p. 1091-6.
14.       Chang, M.H., et al., Decreased incidence of hepatocellular carcinoma in hepatitis B vaccinees: a 20-year follow-up study. J Natl Cancer Inst, 2009. 101(19): p. 1348-55.
15.       The GlaxoSmithKline Vaccine HPV-007 Study Group (2009) Sustained efficacy and immunogenicity of the human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine: analysis of a randomised placebo-controlled trial up to 6·4 years. Lancet Volume,  DOI: 10.1016/S0140-6736(09)61567-1
16.       Flossmann, E. and P.M. Rothwell, Effect of aspirin on long-term risk of colorectal cancer: consistent evidence from randomised and observational studies. Lancet, 2007. 369(9573): p. 1603-13.
17.       Cuzick, J., et al., Long-term results of tamoxifen prophylaxis for breast cancer--96-month follow-up of the randomized IBIS-I trial. J Natl Cancer Inst, 2007. 99(4): p. 272-82.
18.       Martino, S., et al., Continuing outcomes relevant to Evista: breast cancer incidence in postmenopausal osteoporotic women in a randomized trial of raloxifene. J Natl Cancer Inst, 2004. 96(23): p. 1751-61.
19.       Beral, V., et al., Ovarian cancer and oral contraceptives: collaborative reanalysis of data from 45 epidemiological studies including 23,257 women with ovarian cancer and 87,303 controls. Lancet, 2008. 371(9609): p. 303-14.