What is the earliest age at which someone could be diagnosed with colon cancer? I am 26, but my grandmother and both of her siblings have had colon cancer. Is this something that I can wait until I am 40 to get tested, or should I be concerned now?

G.J.

Colon cancer is the second leading cause of cancer death in the United States after lung cancer. The risk for colon cancer rises with age, with more than 90 percent of cases occurring in people over the age of 50. However, it is important to note that colon cancer has been detected in people of all age groups.

In fact, in one hereditary condition, known as familial adenomatous polyposis, patients develop hundreds of colon polyps at a very young age and colon cancer often appears before age 20. Keep in mind that this and other hereditary colon cancer syndromes are rare. Most colon cancer is sporadic -- that is, having no strong hereditary pattern.

Recommendations for colon-cancer screening include yearly stool tests for trace amounts of blood and a flexible sigmoidoscopy examination every three to five years beginning at age 50 for the general population. In patients with a higher risk of colon cancer, earlier or more frequent screening may be recommended. Such patients include those who have colitis, those who have already had colon cancer and those who have a family history of colon cancer. In someone has a parent, sibling or child with colon cancer, it is recommended that screening with a full colonoscopy begin when the person is 10 years younger than the age at which his or her relative was diagnosed with cancer, or at age 50, whichever age is lower. Thus, if a family member was diagnosed with colon cancer at age 45, the person should be screened starting at age 35.

Although none of your parents or siblings have developed colon cancer, you still face a higher-than-average risk since your grandmother and two of her siblings have had colon cancer. The time to begin screening for you will depend on the ages at which they were diagnosed, but will obviously be no later than age 50. You should make an appointment with a gastroenterologist to discuss your family history of colon cancer and the recommendations for screening in your particular case.