Cancer of the colon and rectum (colorectal cancer) is the second most common causes of fatal cancer.  Close to 20,000 Canadians are diagnosed with the condition each year. If identified early enough, this type of cancer is curable.

The currently recommended tests for the detection of colorectal cancer are: (1) to report to your physician any significant change in your bowel habits, (2) to have a regular physical examination over the age of 50 that includes a digital rectal examination, (3) an annual stool examination looking for trace amounts of blood in persons over 50.

There are a number of new, more sensitive and specific screening tests of colorectal cancer that will soon become available.

Some 3-5% of all colorectal cancers occur in persons with the hereditary condition known as Hereditary Non-polyposis Colorectal Cancer (HNPCC) of Lynch Syndrome. Recent developments have shown that mutations in either of two genes, the MLH1 and MLH2 are responsible for this syndrome.  This syndrome and its testing are covered in another section of this web site.

An important test for monitoring the treatment of colorectal cancer in the CEA (or Carcinoembryonic Antigen).

Cancer of the colon (large intestine) commonly secretes a protein known as Carcinoembryonic Antigen or CEA. Thus, the blood test for CEA is positive in 70% of patients with such cancers.  High values of CEA are found with metastatic spread of the cancer to other parts of the body. Persisting elevated or progressively rising levels of CEA after surgical treatment usually indicate incomplete surgical resection.

CEA tests are not recommended for screening for cancer. They are measured before an operation for bowel cancer in selected cases. Following surgery it is recommended that CEA levels be monitored every 2 to 3 months for at least 2 years.

The CEA is raised in conditions other than colon cancer. Smokers have increased values by about 10%. Increases are seen in other forms of cancer (lung, pancreas, stomach, breast), and in various non-cancerous conditions (hepatitis, emphysema, cirrhosis, ulcerative colitis, Crohn’s disease, pulmonary infections, gastritis, gastric ulcer, pancreatitis, polyps of the colon and rectum, diverticulitis, Crohn's disease, benign prostatic hypertropy and renal disease.

Should CEA Be Used In Cancer Screening?

There is a major overlap in the distribution of plasma CEA values in subjects with inflammatory diseases and benign and malignant tumors of the gastrointestinal tract and of other sites, including breast, bronchus, urothelium, ovary, uterus, and cervix. Therefore, the plasma CEA assay is not diagnostic enough to discriminate between localized malignant tumors and benign disorders. For this reason  serum CEA assays are not recommended for screening asymptomatic patients for cancer.

Is CEA Helpful In Cancer Diagnosis?

CEA cannot be used independently to establish a diagnosis of cancer. However, in a patient with symptoms, a grossly elevated value, greater than 5-10 times the upper limit of the reference normal range should be considered strongly suggestive for the presence of cancer.

Is CEA Helpful In Monitoring Cancer Treatment?

The regular and sequential assay of plasma CEA is the best presently available noninvasive technique for postoperative surveillance of patients to detect recurrence of colorectal cancer. As a monitor of colorectal cancer, CEA has been found to be elevated when residual disease is present or is clinically progressing. Following complete surgical removal of a colorectal malignancy, an elevated plasma CEA value should usually return to a normal value by 6 weeks. The failure to observe a reduction of a previously elevated preoperative CEA titer strongly indicates the presence of residual tumor. It is also possible to demonstrate in a substantial number of patients that CEA becomes significantly elevated before metastatic disease can be detected by clinical or other diagnostic measures. This information can be achieved by obtaining plasma samples for CEA assay preoperatively, 4 to 6 weeks postoperatively, and thereafter at regular intervals as an integral component of overall patient follow-up. While slowly rising levels may be more indicative of local recurrence, rapidly rising values reaching very high levels, usually in excess of 20 mg/L, are found most often with hepatic and bone metastases.

For patients with metastatic tumor, the CEA assay may complement standard clinical measurements of tumor response to therapy recognizing at all times that there may not be a strict correlation.

Inherited Cancer
For information about inherited cancer of the bowel see the discussion of Colaris in the Inherited Cancer section of this website.