Dear Dr. B: I have a strong family history of colon cancer. I would like a blood test done every year for early detection of colon cancer. What about CEA blood test that colon cancer patients get so frequently? Why cannot my family doctor order this test for me to make my life easy? Asks Mr. C.
Dear Mr. C: CEA stands for carcinoembryonic antigen. This test has been available for 35 years. It is currently used for patients who have been diagnosed with colon and rectal cancer. Enthusiasm for this test among surgeons and cancer specialists has fluctuated over the years. Originally, the use of this test was poorly controlled. But now the dust has settled and CEA has emerged as the test of choice for patients with colon and rectal cancer.
This test is not good for early detection as there is 30 percent false positive and false negative results in patients who have had no previous colon cancer. Patients with false positive results end up getting many unnecessary investigations. And patients with false negative results may have a false sense of security that they do not have colon or rectal cancer although they may be harbouring one!
CEA is also elevated in other cancers and benign conditions. Therefore, it is hard to be sure if the high level is due to colon and rectal cancer or due to other cancers or benign conditions.
Therefore, the surgeons order CEA after the diagnosis of colon and rectal cancer has been made but before the cancer is resected. CEA provides some idea to the surgeon about prognosis and whether the tumour has already spread. Lower levels indicate limited spread. In about 50 percent of cases, high CEA and increasing CEA after the cancer has been resected, indicates that the cancer has already spread or recurred.
If CEA is high before surgery then it dramatically drops after surgery if the patient has no spread. Then CEA is tested at frequent intervals to see if the level remains the same.
After 33 years of CEA use, the experts have not been able to agree how often CEA should be ordered after successful resection of the cancer. Some do it every month, others every three months for the first two to three years as most recurrences are expected to occur during this critical period. Then the frequency of the blood test is reduced as longer one survives, better the prognosis.
So what is there for early detection of colon and rectal cancer?
Examination of stool for occult blood on regular basis combined with or without endoscopy (flexible sigmoidoscopy or colonoscopy) are currently the best screening tools. Again, each test has its advantages and disadvantages. The optimal method for early detection remains uncertain and peoples compliance rate very poor, as the tests require certain amount of preparation and time. When it comes to colon and rectum, the tests are not very comfortable.
But screening is very important. It has been shown that screening for colon and rectal cancer has reduced mortality by 15 to 33 percent in those who undergo screening routinely. Colon and rectal cancer is the second leading cause of cancer-related deaths in Canada. Therefore, besides screening, early investigation of symptoms like rectal bleeding and change in bowel habit is very important if we want to improve prognosis and survival.
So, Mr. C, discuss with your doctor other methods of early detection as CEA is not a good test for screening for colon and rectal cancer.
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