Epidemiology of Colorectal Carcinoma
More than 300 000 new cases of colorectal cancer are reported annually in the United States and Europe, making it the second most common malignancy in the Western world. In average-risk individuals, the lifetime risk of developing colorectal cancer is 5%–6%. The incidence of the disease increases sharply after age 50. In persons at average risk of colorectal cancer, it is recommended to start screening between the ages of 50 and 60, depending on national screening programs. A positive family history of colon cancer significantly increases the incidence of the disease. If a first-degree relative has had colorectal cancer at any age, the relative risk is 2.25 times greater, which corresponds to a lifetime risk of 12%. If two first-degree relatives have had colon cancer, the relative risk increases to 4.25 times that in the normal population. If a first-degree relative has had colorectal cancer before age 45, the relative risk increases by a factor of 3.87. In such persons it is advisable to begin screening for colorectal cancer 10 years earlier than the age of the diseased relative, for example at age 40 if the first-degree relative was diagnosed with colorectal cancer at age 50.