In the United States, colorectal cancer is most common in adults aged 65 to 74. Rates of new colorectal cancer cases are decreasing among adults aged 50 years or older due to an increase in screening and to changes in some risk factors (for example, a decline in smoking) (2). However, incidence is increasing among younger adults (2–4) for reasons that are not known.
An analysis of US population-based cancer registry data from NCI’s Surveillance, Epidemiology, and End Results (SEER) program for 2000 to 2014 shows that, each year over this period, the incidence of colorectal cancer increased 2.7% among 20- to 39-year-olds and 1.7% among 40- to 49-year-olds while decreasing 0.5% among 50- to 59-year-olds, 3.3% among 60- to 69-year-olds, and 3.8% among 70- to 79-year-olds (5).
Although the percentage increases were higher in the younger age groups than the older age groups, fewer colorectal cancers were still diagnosed in younger people than older people (for example, for 2000 to 2014, 22.5 colorectal cancers were diagnosed per 100,000 people aged 40 to 49 years, compared with 128.6 colorectal cancers diagnosed per 100,000 people aged 60 to 69 years).
The major risk factors for colorectal cancer are older age and having certain inherited conditions (such as Lynch syndrome and familial adenomatous polyposis), but several other factors have also been associated with increased risk, including a family history of the disease, excessive alcohol use, obesity, being physically inactive, cigarette smoking, and, possibly, diet.
In addition, people with a history of inflammatory bowel disease (such as ulcerative colitis or Crohn disease) have a higher risk of colorectal cancer than people without such conditions.