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Colon Cancer

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Screening Tests for Early Detection

CAP Reminder ServiceIt is recommended that all adults begin regular colon cancer screening when they turn 50. Deciding which screening test to use and how often ultimately depends on a person's individual risk of colon cancer. If a first-degree relative has had colon cancer, for instance, screening should start 10 years prior to the age that relative was diagnosed to help identify possible pre-cancerous polyps.

In March 2008, screening guidelines for the early detection of pre-cancerous polyps and colon cancer were released jointly by the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. These guidelines divide screening options into two categories: 1) full or partial structural exams that inspect the colon itself and can detect both cancer and precancerous polyps and 2) laboratory tests on stool samples that detect blood that is possibly caused by existing cancer or that detect cancerous cells shed in the stool. Another difference between these screening options is that direct examinations such as sigmoidoscopy and colonoscopy allow for removal of polyps at the time the test is done. All other tests must be followed up with another procedure to remove any suspected growths.

Imaging Tests

These tests visualize the colon and can detect both pre-cancerous polyps and existing cancers.
TestDescriptionRecommended Screening IntervalProsCons
Sigmoidoscopy Examination of the rectum and lower colon with a rigid or flexible lighted instrument Every 5 years Minimal preparation ahead of time

Does not usually need sedation

Fairly quick and safe
Only examines about 30% of colon
Can’t remove all polyps

Small risk of bleeding, infection or bowel tear

May need to have colonoscopy if abnormal result found
Colonoscopy Examination of the rectum and entire colon with a lighted instrument Every 10 years Can examine the entire colon

Can remove polyps and take biopsies for pathological testing
Extensive full bowel preparation ahead of time

Sedation needed to perform

Takes at least one to two days for prep and recovery

Risk of bleeding, infection or bowel tears
Double contrast barium enema Series of x-rays of the colon and rectum; patient is given an enema with a white, chalky solution that outlines the colon and rectum on the x-rays; tube inserted in rectum, bowel is inflated with air Every 5 years Does not require sedation

Can view entire colon

Relatively safe; minimal risk of tear to colon
Same full bowel preparation needed as for colonoscopy

Cannot remove polyps

May need to have colonoscopy if suspicious results found
Virtual colonoscopy (CTC, or Computed Tomographic Colonography) Examination of the rectum and entire colon to the small intestine using x-rays and computers; tube inserted in rectum and bowel is inflated with air Every 5 years No sedation required

Can view entire colon

Relatively safe; minimal risk of tear to colon
Full bowel preparation required

Cannot remove polyps

May need colonoscopy if abnormal results

Laboratory Tests

These tests are performed on stool samples and can detect existing cancers.
PurposeDescriptionRecommended Screening IntervalProsCons
Guaiac-based fecal occult blood test (gFOBT) Test to detect hidden blood in stool sample Annually No bowel preparation

No direct risk to bowel

Sample can be collected at home
Dietary restriction before testing

Cannot detect precancerous changes

Detects any blood in colon, not just from cancers but from food or dental procedures
Fecal Immuno-chemical test (FIT or iFOBT) Test to detect hidden blood in stool sample; different collection technique than gFOBT Annually No dietary or drug restrictions

No bowel preparation

No direct risk to bowel

Sample can be collected at home
Cannot detect precancerous changes

May miss some cancers; one time testing not effective
DNA test Detects mutations in a specific gene associated with colon cancer in DNA isolated from a stool sample Not defined at this time; more scientific evidence needed to develop a recommendation No bowel preparation or dietary restrictions

Sample can be collected at home

No risk of bowel tear
Cannot detect precancerous changes

Adequate stool sample must be obtained

Special handling needed

In addition to these, a physician may perform a digital rectal examination (DRE) to feel for a rectal mass with a gloved finger. Most colon cancers, however, are beyond the reach of a finger and have no symptoms.

If a test other than colonoscopy gives a result suggestive of polyps or cancer, a full colonoscopy is often done to examine the full colon and collect tissue samples (biopsies) of polyps or potentially cancerous areas.

Tests for Diagnosis, Staging, and Prognosis
Biopsy:
When a suspected cancer is found during a colonoscopy, a biopsy is taken, removing some tissue from the suspicious site for examination under a microscope by a pathologist.

Drawing of a colon polyp and two normal intestinal folds             Drawing of a colon polyp being removed

If the tissue is cancerous, the next step is to determine the stage (or extent) of disease. Treatment will depend in part on the "stage" of the colon or rectal cancer; it is categorized by how far it has spread from its original site. Staging systems for colon cancer vary in different parts of the world, and some use letters instead of numbers. One common system used to describe colon cancer stages is:

  • Stage 0: Very early cancer on the innermost layer of the colon or rectum (carcinoma in situ)
  • Stage I: Tumor in the inner layers of the colon but has not grown through the wall of the colon
  • Stage II: Tumor in the outer layers of the colon and/or nearby tissue but has not spread to lymph nodes
  • Stage III: Tumor that has spread to the lymph nodes but not to distant organs of the body
  • Stage IV: Tumor that has spread to distant organs, such as the lungs, bone, or liver (metastatic)

Other laboratory tests:

  • A laboratory test for carcinoembryonic antigen (CEA) may be ordered to help in staging. This protein is increased in many people with colon cancer, and blood levels generally correlate with the stage of the disease. CEA testing also can help in determining prognosis, as increased concentrations are associated with an increased risk of recurrence and development of metastatic disease.
  • A test for epidermal growth factor receptor (EGFR) may be performed on a sample of the tumor to help establish a prognosis and guide treatment. Tumors that express EGFR tend to be more aggressive, but treatment can be targeted toward this type of tumor; an EGFR blocking agent may be used as therapy.
  • A test to detect a KRAS gene mutation in tumor tissue may be used to guide cancer treatment and to evaluate prognosis. The presence of certain mutations indicates that anti-EGFR drug therapy will not be effective in treating the cancer and a likely poorer prognosis.

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