Diagnosis of Colorectal Cancer

Most colorectal cancers are malignancies of the cells that line the interior of the colon and rectum. If tests indicate the presence of colorectal cancer, additional examinations are performed to determine the extent or stage of the disease:

Imaging Tests

Radiological tools used to diagnose and stage colorectal cancer include:

  • Computed tomography (CT)
  • Magnetic resonance imaging (MRI)
  • Chest X-ray
  • Positron-emission testing (PET scan)
  • Ultrasound

Learn more about Diagnostic Imaging Resources at Greenwich Hospital


A biopsy involves removing a small tissue sample for a pathologist to examine under a microscope for cancer cells. This can take place during a colonoscopy or surgery.

Blood Tests

Blood tests are performed to check for the presence of CEA, a protein that acts as a marker for colorectal cancer. The CEA test is often used to diagnose a possible recurrence in people who have had colorectal cancer in the past. The CEA test does not diagnose early colon cancer and is not a substitute for colonoscopy.


Physicians may perform an angiography to find blood vessels next to a cancer that has spread to the liver. This information is used to plan surgery that minimizes blood loss.