Understanding statistics about new discoveries in the treatment and prevention of cancer can be confusing. From one day to the next, we read about the results of scientific studies that contradict each other. It can be difficult to determine what you should do to lower your risk of developing cancer.

Risk is the probability or chance that an event might or could occur, not that it will occur. For example, when you flip a coin you have a one chance in two (or a 50 percent chance) that the coin will land heads up.

When you read about risk of developing cancer or other diseases, the numbers come from studying large groups of people to determine what the probability is that any given person or group of people will develop the disease over a period of time.

Absolute risk means the actual probability that a person will develop cancer during a certain time period such as, by age 50 or lifetime risk. Lifetime risk means the probability of someone developing cancer over their entire lifetime.

Relative risk compares two people’s risk, rather than focusing on a person’s absolute risk. Scientists determine relative risk by comparing how many people have cancer in Group 1 versus how many people have cancer in Group 2. The people in Group 1 are in that group because they share a certain behavior or trait in common, and Group 2 contains people who do not share that same trait. For example, according to the 2004 Surgeon General’s report on the health consequences of smoking, men who smoke are about 23 times more likely to develop lung cancer than men who have never smoked.

For more information about cancer risk or prevention, or any cancer concern, contact:

Cancer Information Service
Holden Comprehensive Cancer Center
UI Hospitals and Clinics
200 Hawkins Drive, 4802 JPP
Iowa City, Iowa 52242
Toll-free: 1-800-237-1225
cancer-information@uiowa.edu