Rectal Cancer

Diagnosis begins with routine screening tests, including digital rectal examination (DRE) and colonoscopy. Your provider may do a biopsy during your colonoscopy to obtain tissue samples for examination by a pathologist.

If lab tests detect cancer, your provider may refer you to an oncologist for additional tests. Those tests may include blood tests, imaging tests, procedures to confirm diagnosis, and lab tests for closer examination of cancerous cells in tissue samples.

Blood tests

Your oncologist may order the following blood tests to look for signs of rectal cancer:

• Complete blood count (CBC): A medical pathologist may check your red blood cell levels for signs of anemia.
• Comprehensive metabolic panel (CMP): This test measures many substances in your blood, including ones that show how well your kidneys and liver are functioning.
• Liver enzyme test: This test checks for signs that rectal cancer is in your liver.
• Tumor marker tests: A tumor marker is a substance that cancerous cells may release in your blood. In rectal cancer, a medical pathologist will look for signs of carcinoembryonic antigens (CEA).

Diagnostic procedures

Tests may include a diagnostic colonoscopy, which follows up on the test that detected abnormalities in your rectum. They may order a proctoscopy to look inside your rectum.

Imaging tests

Your oncologist may order the following imaging tests to determine if cancer is spreading (metastasizing) from your rectum to other areas of your body:

• Computed tomography (CT) scan.
• Magnetic resonance imaging (MRI) tests.
• Pelvic ultrasound.

Your oncologist will use test results to establish the cancer stage. Rectal cancer is categorized into five different stages:

• Stage 0: Screening tests detect cancerous cells on the surface of tissue lining your rectum.
• Stage 1: The tumor grows below the lining and possibly into your rectal wall.
• Stage 2: The tumor grows into your rectal wall and might extend into tissues around your rectum.
• Stage 3: The tumor invades your lymph nodes next to your rectum and some tissues outside of your rectal wall.
• Stage 4: The tumor spreads to distant lymph nodes or organs.