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What is a risk factor?

Cancer risk refers to a person’s chance of developing cancer. A risk factor is any substance or condition that increases the risk of developing cancer.

There are very few cancers that have a single, known cause. Most cancers seem to be the result of a complex mix of many risk factors. These risk factors may play different roles in starting cancer and helping it grow. Some risk factors include heredity (genetics), lifestyle choices and exposure to cancer-causing substances (carcinogens) in the environment.

  • In general, the more often and the longer the exposure to a risk factor, the greater the chance that cancer will develop.
  • It can take many years for cancer to develop after exposure to a risk factor.
  • Cancer usually develops after exposure to many risk factors over time. People may be exposed to several risk factors in the course of their daily lives.
  • Some people have a higher risk of developing cancer because of certain risk factors. Even if a person has one or more risk factors, it is impossible to know exactly how much these factors may contribute to developing cancer later in life.
  • People at low risk may get cancer, while people at high risk may not get cancer.
    • Low risk does not mean that a person will not get cancer. It means that there is less chance of getting cancer.
    • High risk means that the chances of getting cancer may be greater, but it does not mean that cancer will develop. It isn’t always clear why one person gets cancer and another doesn’t.

Reviewing the scientific evidence on risks

Over the years, researchers have developed a better understanding of how cancers develop and grow. Researchers look at all the scientific information to determine whether a substance causes, or could cause, cancer. Scientists carefully review evidence from studies done in people and in the laboratory to determine whether a substance may increase the risk of cancer.

Scientists usually look at 3 things to determine if something is a risk factor for cancer:

  • How much, how often and under what circumstances people are exposed to a particular substance. Scientists are more confident that exposure is directly related to cancer risk when:
    • the risk of cancer increases as exposure increases
    • the risk of cancer decreases as exposure decreases
  • How strong and how consistent the relationship is between exposure and the risk of developing cancer.
  • How similar the findings are in studies done in people and in the laboratory. When these studies come to similar conclusions, scientists are more confident about the relationship between exposure to a substance and its role as a risk factor for cancer.

Cancer risk assessment

People are often concerned about their personal risk of developing cancer. Risk assessment involves looking at information about a person (such as their age, health history, family history, lifestyle and diet choices) to estimate their cancer risk. Knowing your risk factors can help you make personal health choices to reduce your risk of developing certain cancers. Doctors use a variety of risk assessment tools to estimate a person’s risk of developing cancer.

Reducing your risk

You can avoid some risk factors, such as tobacco. Other risk factors, like age or certain genes, cannot be avoided. Risk reduction (or prevention) means taking action to lower the risk of developing cancer. About half of all cancers can be prevented through healthy living and policies that protect the public.

There are things you can do to lower your overall chance of developing certain types of cancer and stay well. For example, eating a healthy diet that includes a variety of vegetables and fruit each day may reduce the risk of cancer.

Even people who make healthy choices and do everything they can to reduce their risk can develop cancer. Some people develop cancer without having any identifiable risk factors.


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Making progress in the cancer fight

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The 5-year cancer survival rate has increased from 25% in the 1940s to 60% today.

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