Understanding risk factors
A cancer risk factor 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.
Knowing your risk factors and discussing them with your healthcare team is essential. 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 counselling (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 behaviours. 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 the following:
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 remove their breasts to prevent cancer. This surgery appears to lower the risk of breast cancer by at least 95%. Also, these women may 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 counsellor can discuss getting specific genetic tests. They can tell you your risk of getting cancer based on your family history and other factors.
Understanding the difference between absolute and relative risk
Doctors use absolute and relative risk to assess if a person's risk is higher or lower than that of the general population or a specific group.
Absolute risk is the chance of a person developing a disease during a given time. This identifies how many people are at risk for 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. For example, absolute risk cannot show if a group of older women has a higher risk of breast cancer than younger women.
Relative risk compares the risk of disease between two groups of people. It resembles one group with a specific risk factor for a disease to another group’s threat.
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 particular risk factor for breast cancer. The other group of women does not have this risk factor. Researchers track how many people from each group develop cancer over time. Let’s say they find that 2 women with 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. However, the absolute risk would be 2% or 2 out of 100 people.
Patients can use risk measurements to make better lifestyle choices or cancer screening choices. 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, ensure you find the absolute risk. Most research studies report relative risks. This can make the risk sound higher than it actually is.
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