Understanding Cancer Risk

Approved by the Cancer.Net Editorial Board, 03/2018

Risk is the chance that an event will happen. When talking about cancer, risk is most often used to describe the chance that a person will get cancer. It is also used to describe the chance that the cancer will come back or recur.

Researchers and doctors use cancer risk to improve the health of many people. One example of this is understanding the risks from smoking. Scientists discovered that smoking increases the risk of lung cancer. They used this knowledge to launch a global anti-smoking campaign to help save lives.

Understanding risk factors

A cancer risk factor is anything that increases a person’s chance of getting cancer. Yet most risk factors do not directly cause 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. It will help you make better lifestyle choices to improve your health. This information could also help your doctor decide if you need genetic testing and counseling (see below).

General risk factors for cancer include:

Older age
A personal or family history of cancer
Using tobacco
Obesity
Alcohol
Some types of viral infections, such as human papillomavirus (HPV)
Specific chemicals
Exposure to radiation, including ultraviolet radiation from the sun

You can avoid some risk factors by stopping risky behaviors. These include using tobacco and alcohol, being overweight, and getting multiple sunburns. Other risk factors cannot be avoided, such as getting older. Learn about the risk factors for certain types of cancer.

Risk factors and cancer screening

Understanding your risk for cancer can help your doctor decide whether 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
Surgery or medication to lower your cancer risk

For example, a woman whose mother had breast cancer is at least twice as likely to have breast cancer than a woman who does not have the same family history. Some women 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 remove their breasts to prevent cancer. This surgery appears to lower the risk of getting breast cancer by at least 95%. Also, these women may choose to take medicine to lower the risk of breast cancer.

People with a strong 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.

Understanding the difference between absolute and relative risk

Doctors use absolute risk and relative risk to assess if a person's risk is higher or lower than that of either the general population or a certain group of people.

Absolute risk is the chance that a person will develop a disease during a given time. This identifies how many people are at risk for a disease in the general population.

For instance, consider the statement “1 out of 8 women (12.5%) will get breast cancer in her lifetime.” This describes the absolute risk for the general population of women. It cannot identify the risk for a certain person or group of people. For example, absolute risk cannot show if a group of older women has a higher risk of breast cancer than a group of younger women.
Relative risk compares the risk of disease between two groups of people. It compares one group with a certain risk factor for a disease to another group’s risk.

For instance, imagine you are comparing the risk of breast cancer among 2 groups of 100 women. But only the women in 1 group have a certain risk factor for breast cancer. The other group of women does not have this risk factor. Researchers keep track of how many people from each group develop cancer over a certain time. Let’s say they find that 2 women who have the same risk factor get cancer. But only 1 woman without this risk factor gets cancer. Then those in the first group have 2 times the risk of the second group. This is a 100% increase in relative risk. The absolute risk, however, would be 2% or 2 out of 100 people.

Patients can use risk measurements to make better choices about lifestyle changes or cancer screening. It is also important to know the difference between absolute and relative risk. For instance, the relative risk in the last example might sound high. It identified a person’s relative risk of developing cancer by 100%. But look at the absolute risk to get a more complete picture. That is, 1 person in 100 compared to 2 people in 100. If you want to compare the research you hear about in the news to your own situation, make sure you find the absolute risk. Most research studies report relative risks. This can make the risk sound higher than it actually is.

Questions to ask your health care team

Statistical language can be hard to understand. So ask your health care team to explain what this information means in your situation. Consider bringing up these questions about cancer risk:

What risk factors do I have? How do they affect my risk of cancer?
What is my chance of developing cancer in the next 5 years? In my lifetime?
What can I do to lower my risk of cancer?
What if I change my behavior to eliminate a risk factor (for example, quit smoking or lose weight)? Then what are my chances of getting cancer in the next 5 years? In my lifetime?
What if I find out about a new risk factor, such as a relative developing cancer? Then how much does the risk increase?
What cancer screening tests do you recommend? How often should I have them?