Cancer usually develops in older people 87% of all cancers in the United States are diagnosed in people 50 years of age or older. Certain behaviors also increase risk, such as smoking, eating an unhealthy diet, or not being physically active.
In the US, approximately 40 out of 100 men and 38 out of 100 women will develop cancer during their lifetime. These probabilities are estimated based on cancer occurrence in the general population and may overestimate or underestimate individual risk because of differences in exposures (e.g., smoking), family history, and/or genetic susceptibility.
Relative risk is the strength of the relationship between exposure to a given risk factor and cancer. It is measured by comparing cancer occurrence in people with a certain exposure or trait to cancer occurrence in people without this characteristic.
For example, men and women who smoke are about 25 times more likely to develop lung cancer than nonsmokers, so their relative risk of lung cancer is 25. Most relative risks are not this large.
For example, women who have a mother, sister, or daughter with a history of breast cancer are about twice as likely to develop breast cancer as women who do not have this family history, in other words, their relative risk is about 2.
For most types of cancer, risk is higher with a family history of the disease, which is thought to result from the inheritance of genetic variations that confer low or moderate risk and/or similar exposures to lifestyle/environmental risk factors among family members.
Only a small proportion of cancers are strongly hereditary, meaning they are caused by an inherited genetic alteration that confers a very high risk.
What Percentage of People Survive Cancer?
Over the past three decades, the 5-year relative survival rate for all cancers combined increased 20 percentage points among whites and 24 percentage points among blacks, yet it remains substantially lower for blacks (70% versus 63%, respectively).
Improvements in survival reflect improvements in treatment, as well as earlier diagnosis for some cancers. Survival varies greatly by cancer type and stage at diagnosis.
Relative survival, the survival statistic used throughout this report, is the proportion of people with cancer who are alive for a designated time (usually 5 years) after diagnosis divided by the proportion of people of similar age, race, etc. expected to be alive in the absence of cancer based on normal life expectancy.
Relative survival does not distinguish between patients who have no evidence of cancer and those who have relapsed or are still in treatment, nor does it represent the proportion of people who are cured because cancer death can occur beyond 5 years after diagnosis.
Although relative survival rates provide some indication about the average experience of cancer patients in a given population, they should be interpreted with caution for several reasons. First, 5-year survival rates do not reflect the most recent advances in detection and treatment because they are based on patients who were diagnosed several years in the past.
Second, they do not account for many factors that affect individual survival, such as treatment, other illnesses, and biological or behavioral differences. Third, improvements in survival rates over time do not always indicate progress against cancer.
For example, increases in average survival rates occur when screening results in the detection of cancers that would never have caused harm if left undetected (over diagnosis) and early diagnosis that does not increase lifespan.