Tests to evaluate colorectal cancer include:
A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis of colorectal cancer. A biopsy may be performed during a colonoscopy, or it may be done on any tissue that is removed during surgery. Sometimes a CT scan or ultrasound is used to perform a needle biopsy.
Because colorectal cancer often bleeds into the large intestine or rectum, people with the disease may become anemic. A test of the number of red cells in the blood, which is part of a complete blood count (CBC), can indicate that bleeding may be occurring. Another blood test detects the levels of a protein called carcinoembryonic antigen (CEA). High levels of CEA may indicate that a cancer has spread to other parts of the body. CEA is not an absolute test for colorectal cancer because it is elevated in only about 60% of people with colorectal cancer that has spread to other organs from the colon. CEA tests are most often used to monitor patients already treated for colorectal cancer.
Computed Tomography (CT) Scan
A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then puts these images into a detailed, cross-sectional view that shows any abnormalities or tumors. In a person with colon cancer, a CT scan can check for the spread of cancer in the lungs, liver and other organs.
Ultrasound is a procedure that uses sound waves to produce images of the body to tell if cancer has spread to the liver or other organs. An endorectal ultrasound is commonly used to determine the depth of penetration of rectal cancer, and can be used to aid in planning treatment; however, this test cannot accurately detect metastatic lymph nodes or metastatic diseases beyond the pelvis.
An x-ray is a picture of the inside of the body. A chest x-ray may be used to see if cancer has spread to the lungs.
Positron Emission Tomography (PET) Scan
In a PET scan, radioactive sugar molecules are injected into the body. Cancer cells absorb sugar more quickly than normal cells, so they light up on the PET scan. PET scans are often used to complement information gathered from CT scan and physical examination.