Understanding Cancer Risk

Aprobado por la Junta Editorial de Cancer.Net, 08/2022

Risk is the chance that an event will happen. "Cancer risk" is most often used to describe the chance that a person will develop cancer. In cancer care, this phrase is also used to describe the chance that the cancer will come back after treatment. When cancer returns, it is called a recurrence.

Research about cancer risk helps improve the health of many people. For example, when scientists discovered that smoking increases the risk of lung cancer, anti-smoking campaigns began and have helped save many lives.

It is also important for people to understand their personal risk of developing cancer. Knowing your individual risk factors can help you make decisions about your health and habits that can reduce your risk of developing cancer and/or increase your chance of finding cancer in an earlier stage. Cancer that is found in an earlier stage may be easier to treat or have a better prognosis.

This article will help you understand how doctors and researchers calculate cancer risk and explains common cancer risk factors.

What is the difference between absolute risk and relative risk?

Doctors and researchers use two different risk factor calculations to understand cancer risk: absolute risk and relative risk. Understanding absolute risk and relative risk can help you get a clear picture of your personal risk, which can help you make health care and lifestyle decisions.

Absolute risk tells you the average person's chance of developing cancer during a specific period of time. For example, the lifetime risk of an average person developing colorectal cancer is around 4.1%. In other words, about 1 in 24 people will develop colorectal cancer in their lifetime.

Absolute risk cannot tell you the risk for a specific person or a specific group of people.

Relative risk compares one group's risk of developing cancer with another group. For example, research shows that people with diabetes have a 38% higher risk of developing colorectal cancer.

It is important to remember that this does not mean that a person with diabetes has a 38% chance of developing colorectal cancer in their lifetime. It means that there is a 38% increase over the absolute risk (4.1%). The increase in risk for a person with diabetes of developing colorectal cancer is 1.6%, which means their lifetime risk is 5.7%.

To calculate the increase in absolute risk, in this specific example, you first need to find out what 38% of 4.1% is. You can do this by converting the percentages to decimals: 0.38 x 0.041 = .016. Then add together the original absolute risk (4.1%) and the increase in risk (1.6%) to get the new lifetime risk of 5.7%.

Both absolute risk and relative risk are important when you are considering your own risk of developing cancer. You can use these risk measurements to know if or when you need certain types of cancer screening or to make healthy lifestyle choices. If you want to compare any research you hear about in the news to your own situation, make sure you find the data about the increase in absolute risk. Most research studies and the news stories report relative risk. This can make it seem like your risk of developing cancer is higher than it actually is.

And, always talk with your doctor about what you are hearing about new research about cancer risk and about your personal cancer risk. Ask about any new terms that you don't understand. This helps you have clear information about your cancer risk and your doctor's recommendations about the best screening schedule or other health care decisions for you. Your health care team can also guide you about such healthy habits as how to quit smoking, getting regular exercise, and eating healthy foods.

What are common cancer risk factors?

A cancer risk factor is anything that increases a person's risk of developing cancer. Most risk factors do not directly cause cancer.

Having a risk factor does not mean that you definitely develop cancer. Some people with several risk factors never develop cancer. And others with no known risk factors do.

It is important to know your risk factors and talk about them with your health care team. Knowing this information can help you make medical and lifestyle choices to improve your health. It can also help your health care team decide if you need genetic testing and counseling (see below).

General risk factors for cancer include:

Some risk factors can be avoided or used in moderation. Other risk factors cannot be avoided, such as getting older. It is important to remember that it is not just the type of risk factor, but the amount of exposure, how often, and when the exposure happens. For example, weight gain after menopause is linked to a higher breast cancer risk.

The listed items above are not the only risk factors for cancer. There are more specific risk factors for specific types of cancer. Learn more in this website's guides to specific types of cancer, each of which has a section explaining known risk factors for each disease.

Cancer risk factors and cancer screening

Understanding your personal risk for cancer can help your health care team decide if you could benefit from:

  • A cancer screening test, such as a mammogram or colonoscopy

  • A screening test at an earlier age and more often than routine screening

Screening increases the chance of finding a cancer or precancerous areas when they are smaller and usually easier to treat. If you do not get recommended screening, you may miss the chance to find a cancer in an earlier stage.

If you are at a high risk of developing cancer, there may be surgery or medication that can lower your cancer risk. For example, some people are at a higher risk of developing breast cancer because their mother, father, or other close relative had breast cancer. Some people have strong family histories or genetic mutations linked to breast cancer. Since they are at a very high risk of breast cancer, they may choose to have surgery to remove their breasts to prevent cancer. This surgery appears to lower the risk of getting breast cancer by at least 95%. Also, they can choose to take medication to lower the risk of breast cancer. More information about this example can be found in the guide to breast cancer here.

People concerned about their family history of cancer may consider genetic testing. Your doctor or genetic counselor can talk with you about getting certain genetic tests. They can tell you your risk of getting cancer based on your family history and other risk factors.

Questions to ask your health care team

Statistical language can be hard to understand. Ask your health care team to explain what statistical information means for your specific situation. Consider bringing up these questions about cancer risk:

  • What risk factors for cancer do I have? How do they affect my personal risk of developing cancer in the future?

  • What is my chance of developing cancer in the next 5 years? In my lifetime?

  • What can I do to lower my risk?

  • What if I change my behavior to eliminate a risk factor (for example, quit smoking or drinking alcohol)? What would my chances of getting cancer in the next 5 years be? In my lifetime?

  • What can I do to keep myself as healthy as possible and to reduce my cancer risk?

  • What if I find out about a new risk factor, such as a close relative developing cancer? How much would my risk increase?

  • What cancer screening tests do you recommend for me? How often should I have them?

  • Would you recommend genetic testing based on my family's health history?

Related Resources

Understanding Statistics Used to Estimate Risk and Recommend Screening

Changes People Can Make to Lower Their Cancer Risk

Prevention and Healthy Living

How to Talk to Your Kids About Ways to Prevent Cancer

Information about Cancer Risk Factors

More Information

National Cancer Institute: Risk Factors for Cancer