Colorectal Cancer Diagnosis

Colorectal cancer can be identified during a routine screening. In other cases, doctors will order additional tests after discussing symptoms with a patient.

The following tests may be used to diagnose colorectal cancer or find out if it has spread. Tests also may be used to find out if surrounding tissues or organs have been damaged by treatment.

Screening tests

If you are an average-risk individual, it is recommended you start getting regular screenings for colorectal cancer starting at age 45. There are several types of non-invasive colon cancer screening tests that can be taken at home. These tests do not provide a definitive diagnosis for colon cancer, but they can indicate that other, more accurate tests should be used.

There are several types of at-home screening tests:

• Fecal DNA test (FDNA):  This take-home test identifies DNA changes in the cells of a stool sample
• Fecal immunochemical test (FIT): This take-home test identifies blood proteins in stool
• Fecal occult blood test (FOBT): This take-home test identifies blood in the stool

Other, more invasive screening tests for colorectal cancer are endoscopic tests. These procedures are generally performed under some form of sedation so that you do not feel any discomfort. Endoscopic tests allow your doctor to see the inside of your colon clearly.

Endoscopic tests may include:

• Colonoscopy: A tiny camera on flexible plastic tubing (colonoscope) is inserted into the rectum and advanced through the colon. This gives the doctor a view of the entire colon.  Tissue or polyps can be sampled (biopsied) and looked at under a microscope to determine if tumor cells are present.
• Sigmoidoscopy: Similar to colonoscopy but a shorter examination of the rectum and lower colon.

Diagnostic Tests

If you have symptoms of colorectal cancer, or if you have an abnormal screening test result, your doctor may recommend additional tests to more conclusively diagnose cancer and understand its progression. These tests may include:

Blood tests: No blood test can be used to definitively diagnose colon cancer, but they can provide your doctor with additional information about your health, such as your kidney and liver function. Additionally, your blood can be tested for carcinoembryonic antigen (CEA). CEA is a protein, or tumor marker, made by some cancerous tumors. This test also can be used to find out if the tumor is growing, is responding to treatment, or has come back after treatment. 

Imaging tests: Imaging tests can help to provide detailed information about the size or location of colorectal cancer and assess if cancer has spread to other parts of the body. Common imaging tests are:

• CT or CAT (computed axial tomography) scan
• MRI (magnetic resonance imaging) scan including dedicated rectal cancer MRI
• PET/CT (positron emission tomography) scan

Other imaging tests

Virtual colonoscopy or CT (computed tomography) colonoscopy: A focused CT scan of your abdomen and pelvis to create 3-D images, that can show polyps and other abnormalities in your colon and rectum. This test can be used for patients with medical conditions, such as bleeding disorders, that make traditional colonoscopies riskier.

Endoscopic ultrasound (EUS) or endosonography: A flexible tube with an ultrasound device attached to the tip is inserted through the rectum into the colon. The device sends out ultrasound waves to generate images of the colon and nearby tissue. This method helps the physician determine how deeply a tumor invades into the colon wall. It can also be used to examine nearby lymph nodes for cancer spread.

Double contrast barium enema (DCBE): Barium is a chemical that allows the bowel lining to show up on an X-ray. A barium solution is given by enema, and then a series of X-rays are taken.