Can Cancer Be Prevented? What the Research Actually Shows

What people see in the news

Prevention headlines are everywhere: a food that "fights cancer," a supplement that "cuts risk," or a habit that "causes" it. Some of these claims are well supported, and many are not. Sorting them out is easier with a clear source.

What it actually means

The National Cancer Institute defines cancer prevention as action taken to lower the chance of getting cancer. This can include maintaining a healthy lifestyle, avoiding known cancer-causing substances, and taking medicines or vaccines that can prevent cancer from developing.

NCI groups risk factors into those known to increase cancer risk and those that may affect it. Factors known to increase risk include cigarette smoking and tobacco use, certain infections (such as HPV, hepatitis B and C, Epstein-Barr virus, and H. pylori), radiation (including ultraviolet radiation from sunlight and ionizing radiation), and immunosuppressive medicines after an organ transplant. NCI states that scientists believe cigarette smoking causes about 30% of all cancer deaths in the United States.

Factors that may affect risk, according to NCI, include diet, alcohol, physical activity, obesity, diabetes, and environmental exposures.

On what helps, NCI describes interventions known to lower risk, including certain vaccines (for HPV and hepatitis B), some chemoprevention medicines for people at high risk, weight-loss surgery, and — for certain high-risk people — risk-reducing surgery. NCI is also clear about what hasn't been shown to help: it states that aspirin has not been shown to prevent most cancers, and that vitamin and dietary supplements have not been shown to prevent cancer.

What to keep in mind

• Not all risk factors can be changed. NCI notes some, like smoking, can be avoided, while others, like inherited genes, cannot.
• Prevention lowers the chance of cancer; it doesn't guarantee anyone will or won't get it.
• Be cautious with supplement claims. NCI states there isn't enough proof that vitamins or supplements prevent cancer, and that one large trial found vitamin E taken alone increased prostate cancer risk.

Questions to ask a healthcare team

• Which cancer risk factors are most relevant to me?
• Are there vaccines or screenings I should consider based on my situation?
• Do any prevention medicines make sense given my personal risk?
• Is there evidence behind a prevention claim I read about?

Knowing what actually lowers risk — and what doesn't — makes prevention headlines much easier to judge. Free, plain-language cancer education helps more people focus on what the research supports.