My boyfriend's father had colon cancer (not of the genetic variety). My boyfriend has had some inconsistencies with his bowel movements (urgency, diarrhea and constipation). He is opposed to having a rectal exam done. Is there a blood test available to test for colon cancer? Are there any other alternate ways of testing for it?

Elizabeth

The vast majority of cases of colon cancer are not of the genetic variety, and are known as sporadic. I assume you say your friend's father's case is not genetic because no one else in his family has had colon cancer. Even so, regardless of your friend's symptoms, his father's medical history means he will need to have screening exams (colonoscopy) done to look for polyps or cancer.

The age at which he will need to start having these exams depends on the age at which his father was diagnosed. He should have the first screening at an age that is 10 years younger than his father's age when the cancer was detected. The frequency of follow-up exams will depend on what is found in the initial exam.

Your friend has symptoms (diarrhea, urgency) that may be consistent with colitis -- another reason for him to have a colonoscopy. A rectal exam, while an important part of the physical examination in a patient with these symptoms, will not replace the need to visualize his rectum and colon with a colonoscope.

As far as blood tests for colon cancer, the only one available is known as the CEA (carcinoembryonic antigen). This is a test for a protein made by cancerous cells, most often by colon cancer cells. However, it is not very useful as a screening test for two reasons. First, not all colon cancers make this protein. Secondly, other types of cancers can make the protein. Thus, CEA testing is not sensitive enough to pick up all cases of colon cancer, and it is not specific enough to indicate colon cancer as the cause when the protein is found to be is elevated. This test is most useful in patients who've had colon cancer with elevated CEA, in which it is used as a marker following treatment to watch for cancer recurrence.