When doctors talk about risk they are thinking about numbers. Cancer risk numbers are based on reports of cancer from medical facilities. These reports count the total number of people who are diagnosed with a cancer. They also provide information about how many men or women are diagnosed, and their age and race. The risk numbers that come from this information are presented as absolute risk and relative risk.
Other information about risk comes from medical studies. In these studies doctors look at factors such as smoking, diet, or exercise that may affect cancer risk. They draw conclusions about how these and other specific factors affect cancer risk by looking at large groups of people who have a certain risk factor and those who do not. Doctors then look at how many individuals in the two groups are diagnosed with cancer.
By comparing how many people in each of these groups actually develops cancer, doctors are able to estimate relative risk—that is the risk that one group will get cancer compared to another group.
The bottom line is that you can never really know exactly what your individual or personal cancer risk is. What scientists do know is that certain personal characteristics and behaviors increase your chances of getting cancer. These personal characteristics and behaviors are referred to as risk factors.