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.
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.
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.
If you are diagnosed with colorectal cancer, your doctor will determine the stage of the disease. Staging is a way of classifying cancer by how much disease is in the body and where it has spread when it is diagnosed. This helps the doctor plan the best way to treat the cancer. It’s important that staging be performed before treatment begins.
(Source: National Cancer Institute)
Stage 0: Abnormal cells are found in the inner lining of the colorectal tissue. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 also is called carcinoma in situ.
Stage 1: Cancer has formed and spread into the first (submucosa) or second (muscle) layers of the bowel wall. It has not spread outside of the bowel.
Stage 2: Cancer has spread outside of the rectal walls into the surrounding fat or nearby tissue. It has not gone into the lymph nodes. It is divided into stages IIA, IIB or IIC depending on the extent of local tumor involvement.
Stage 3: Cancer has spread to nearby lymph nodes. It has not spread to other parts of the body. It is divided into stages IIIA, IIIB or IIIC depending on the extent of local tumor involvement and the number of lymph nodes that contain cancer.
Stage 4: Cancer has spread to other parts of the body, such as the liver, lungs or ovaries. It is divided into stages IVA,IVB and IVC depending on the number of different other parts of the body or location to which the cancer has spread.
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