Colon Cancer Diagnosis

Good colon cancer outcomes depend on early and accurate diagnosis. At the OHSU Knight Cancer Institute, you get an excellent team and the latest tools. We offer: 

  • Highly trained doctors and other providers who are colon cancer experts.
  • Molecular testing to determine your cancer’s genetic makeup. This helps us match you with the most effective treatments.
  • Team-based care, with specialists who meet weekly to discuss the best treatment options patient by patient.

Overview of colon cancer diagnosis

Any possible sign of colon cancer can bring people to the Knight for diagnostic testing. These signs could be:

  • Pain or discomfort in the belly
  • Changes in bowel habits or appetite
  • Blood in the stool

We have many ways to screen for or diagnose colon cancer. Sometimes, the same tests are used in both. Common diagnostic tools we use are colonoscopy, stool tests and blood tests.

If we find signs that something isn’t right, we can use biopsy, molecular testing or MRI.

Tests to diagnose colon cancer


During a colonoscopy, a doctor guides a thin flexible tube tipped with a camera and light through the anus and into the colon. The doctor looks for cancer and for polyps, abnormal growths on the colon's inside surface. Polyps sometimes turn into cancer. They are often taken out during the procedure.

An illustration shows how a doctor guides a thin tube through the anus to inspect the rectum and colon. The sedated patient lies on their side.  The colon makes an upside-down U shape. The tube travels vertically up the colon, horizontally as the colon travels across the upper belly, and back down to the lower belly.

Stool DNA test

This test checks a stool sample for signs of cancer. Signs can include hidden blood or genetic material that could signal the presence of cancer or polyps. Stool tests can be done at home, but you need a prescription.

Blood tests

Blood tests look for special enzymes or proteins, or for a low red blood cell count, that can signal the presence of cancer.

A fecal occult blood test detects “occult” blood that you can’t see. You can get this at-home test from a doctor or pharmacy. It’s used with other tests to diagnose colon cancer.


If a test shows possible cancer, doctors usually seek a biopsy. A doctor removes a small piece of tissue from the colon so it can be checked for cancer cells under a microscope.

Molecular testing

Knight doctors can use a variety of genetic tests to diagnose colon cancers passed down through families.


An MRI scan (magnetic resonance imaging) uses radio waves and magnets to create precise pictures of the colon. It can be used with other tools to detect cancer.

Learn more

For patients

Call 503-494-7999 to:

  • Request an appointment
  • Seek a second opinion
  • Ask questions


Knight Cancer Institute, South Waterfront

Center for Health & Healing, Building 2
3485 S. Bond Ave.
Portland, OR 97239

Free parking for patients and visitors

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