While colorectal cancer is often found after symptoms appear, most people with early colon or rectal cancer have no symptoms of the disease. Symptoms usually appear only with more advanced disease. This is why getting the recommended screening tests (as described in "Can colorectal polyps and cancer be found early?") before any symptoms develop is so important.

If your doctor finds something suspicious during a screening exam, or if you have any of the symptoms of colorectal cancer described below, your doctor probably will recommend exams and tests to find the cause.

Signs and symptoms of colorectal cancer

If you have any of the following you should see your doctor:

• a change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts for more than a few days
• a feeling that you need to have a bowel movement that is not relieved by doing so
• rectal bleeding, dark stools, or blood in the stool (often, though, the stool will look normal)
• cramping or abdominal (stomach area) pain
• weakness and fatigue

Most of these symptoms are more likely to be caused by conditions other than colorectal cancer, such as infection, hemorrhoids, or inflammatory bowel disease. Still, if you have any of these problems, it's important to see your doctor right away so the cause can be found and treated, if needed.

Medical history and physical exam

If you have any signs or symptoms that suggest you might have colorectal cancer, your doctor will want to take a complete medical history to check for symptoms and risk factors, including your family history.

As part of a physical exam, your doctor will carefully feel your abdomen for masses or enlarged organs, and also examine the rest of your body. Your doctor may also perform a digital rectal exam (DRE). During this test, the doctor inserts a lubricated, gloved finger into the rectum to feel for any abnormal areas.

Blood tests

Your doctor may also order certain blood tests to help determine if you have colorectal cancer.

Complete blood count (CBC): Your doctor may order a complete blood count to see if you have anemia (too few red blood cells). Some people with colorectal cancer become anemic because of prolonged bleeding from the tumor. You may also have a blood test of your liver function, because colorectal cancer can spread to the liver and cause abnormalities.

Tumor markers: Colorectal cancer sometimes produces substances, such as carcinoembryonic antigen (CEA) and CA 19-9, that are released into the bloodstream. Blood tests for these "tumor markers" are used most often with other tests to follow-up patients who already have been diagnosed with or treated for colorectal cancer. They may help show how well treatment is working or provide an early warning of a cancer that has returned.

These tumor markers are not used as screening tests to find cancer in people who have never had a cancer and appear to be healthy, because the tests can't tell for sure whether or not someone has colorectal cancer. Tumor marker levels can be normal in a person who has cancer and can be abnormal for reasons other than cancer. For example, higher levels may be present in the blood of some people with ulcerative colitis, non-cancerous tumors of the intestines, or some types of liver disease or chronic lung disease. Smoking can also raise CEA levels.

Tests to look for colorectal polyps or cancer

If symptoms or the results of the physical exam or blood tests suggest that colorectal cancer might be present, your doctor may recommend more tests. This might include endoscopic tests such as sigmoidoscopy or colonoscopy, or imaging tests such as a barium enema (lower GI series), double-contrast barium enema, or CT colonography (virtual colonoscopy). Most of these tests are described in detail in the section "Can colorectal polyps or cancer be found early?"

Biopsy: Usually if a suspected colorectal cancer is found by any diagnostic test, it is biopsied during a colonoscopy. In a biopsy, the doctor removes a small piece of tissue with a special instrument passed through the scope. Although there may be some bleeding afterward, this usually stops after a short time. Less often, part of the colon may need to be surgically removed to make the diagnosis.

Lab tests of specimens: Biopsy specimens (from colonoscopy or surgery) are sent to the lab where a pathologist, a doctor trained to diagnose cancer and other diseases in tissue samples, looks at them under a microscope. Although other tests may suggest that colorectal cancer is present, the only way to determine this for certain is to look at a specimen under a microscope.

Other lab tests may also be done on biopsy specimens to help better classify the cancer. Doctors may look for specific gene changes in the cancer cells that might affect how they are best treated. For example, many doctors now test the cells for changes in the K-ras gene. This gene is mutated in about 4 out of 10 colorectal cancers. Cancers with these mutations do not benefit from treatment with certain anti-cancer drugs such as cetuximab (Erbitux) and panitumumab (Vectibix).

Imaging tests

Imaging tests use sound waves, x-rays, magnetic fields, or radioactive substances to create pictures of the inside of your body. Imaging tests may be done for a number of reasons, including to help find out whether a suspicious area might be cancerous, to learn how far cancer may have spread, and to help determine if treatment has been effective.

Computed tomography (CT or CAT) scan

The CT scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the part of your body being studied. Unlike a regular x-ray, a CT scan creates detailed images of the soft tissues in the body. This test can help tell if colon cancer has spread into your liver or other organs.

Before the scan, you may be asked to drink a contrast solution and/or get an intravenous (IV) injection of a contrast dye that helps better outline abnormal areas in the body. You may need an IV line through which the contrast dye is injected. The injection can cause some flushing (redness and warm feeling). Some people are allergic and get hives or, rarely, more serious reactions like trouble breathing and low blood pressure. Be sure to tell the doctor if you have ever had a reaction to any contrast material used for x-rays.

CT scans take longer than regular x-rays. You need to lie still on a table while they are being done. During the test, the table moves in and out of the scanner, a ring-shaped machine that completely surrounds the table. You might feel a bit confined by the ring you have to lie in while the pictures are being taken.

In recent years, spiral CT (also known as helical CT) has become available in many medical centers. This type of CT scan uses a faster machine. The scanner part of the machine rotates around the body continuously, allowing doctors to collect the images much more quickly than with standard CT. This lowers the chance of blurred images occurring as a result of breathing motion. It also lowers the dose of radiation received during the test. The biggest advantage may be that the image slices are thinner, which yields more detailed pictures and allows doctors to look at suspicious areas from different angles.

Spiral CT with portography looks specifically at the portal vein, the large vein leading into the liver from the intestine. In this test, contrast material is injected into veins that lead to the liver, to help look for metastases from colorectal cancer to that organ.

CT-guided needle biopsy: CT scans can also be used to precisely guide a biopsy needle into a suspected tumor or metastasis. For this procedure, the patient remains on the CT scanning table, while a radiologist advances a biopsy needle through the skin and toward the location of the mass. CT scans are repeated until the doctors are confident that the needle is within the mass. A fine-needle biopsy sample (tiny fragment of tissue) or a core needle biopsy sample (a thin cylinder of tissue about ½ inch long and less than 1/8 inch in diameter) is then removed and looked at under a microscope.

CT colonography (virtual colonoscopy): CT scans can also be used to perform virtual colonoscopy. This test requires the same type of preparation (cleansing of stool from the colon) as is needed before colonoscopy. Before the scan is done, the colon is inflated with air through a soft flexible tube that is inserted into the rectum so that it can be viewed more clearly; this stretches the colon and can cause some discomfort.

Spiral CT of the abdomen is then done. The thin images it obtains can be combined to create two- and three-dimensional views of the colon and rectum. If abnormalities are detected, a follow-up colonoscopy will be needed to take tissue samples of the abnormal areas.

Ultrasound

Ultrasound uses sound waves and their echoes to produce a picture of internal organs or masses. A small microphone-like instrument called a transducer emits sound waves and picks up the echoes as they bounce off body tissues. The echoes are converted by a computer into a black and white image that is displayed on a computer screen. This test is painless and does not expose you to radiation.

Abdominal ultrasound can be used to look for tumors in your liver, gallbladder, pancreas, or elsewhere in your abdomen, although it can't look for tumors of the colon. For the exam, you simply lie on a table and a technician moves the transducer along the skin overlying the part of your body being examined. Usually, the skin is first lubricated with gel.

Two special types of ultrasound exams are sometimes used to evaluate colon and rectal cancers.

Endorectal ultrasound uses a special transducer that can be inserted directly into the rectum. This test is used to see how far through the rectal wall a cancer may have penetrated and whether it has spread to nearby organs or tissues such as lymph nodes.

Intraoperative ultrasound is done during surgery after the surgeon has opened the abdominal cavity. The transducer can be placed against the surface of the liver, making this test very useful in detecting the spread of colorectal cancer to the liver.

Magnetic resonance imaging (MRI) scan

Like CT scans, MRI scans provide detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays. The energy from the radio waves is absorbed by the body and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material called gadolinium is often injected into a vein before the scan to better see details.

MRI scans are a little more uncomfortable than CT scans. First, they take longer -- often up to an hour. Second, you have to lie inside a narrow tube, which is confining and can upset people with claustrophobia (a fear of enclosed spaces). Newer, more open MRI machines can sometimes help with this if needed. The machine also makes buzzing and clicking noises that you may find disturbing. Some centers provide earplugs to help block this noise out.

MRI scans are sometimes useful in looking at abnormal areas in the liver that might be due to cancer spread. They can also help determine the extent of rectal cancers. To improve the accuracy of the test, some doctors use endorectal MRI. For this test the doctor places a probe, called an endorectal coil, inside the rectum. This must stay in place for 30 to 45 minutes during the test and can be uncomfortable.

Chest x-ray

This test may be done after colorectal cancer has been diagnosed to see if cancer has spread to the lungs.

Positron emission tomography (PET) scan

For a PET scan, you receive an injection of a substance that contains a form of radioactive sugar (known as fluorodeoxyglucose or FDG) into the blood. The amount of radioactivity used is very low. Because cancer cells in the body are growing rapidly, they absorb large amounts of the radioactive sugar. A special camera can then create a picture of areas of radioactivity in the body. The picture is not finely detailed like a CT or MRI scan, but it provides helpful information about your whole body.

A PET scan can help give the doctor a better idea of whether an abnormal area seen on another imaging test is a tumor or not. If you have already been diagnosed with cancer, your doctor may use this test to see if the cancer has spread to lymph nodes or other parts of the body. A PET scan can also be useful if your doctor thinks the cancer may have spread but doesn't know where.

Some newer machines are able to perform both a PET and CT scan at the same time (integrated PET/CT scan). This allows the doctor to compare areas of higher radioactivity on the PET with the more detailed appearance of that area on the CT.

Angiography

Angiography is an x-ray procedure for looking at blood vessels. Contrast medium, or dye, is injected into an artery before x-ray images are taken. The dye outlines the blood vessels on x-ray pictures.

Angiography can be useful in showing the arteries that supply blood to tumors in the liver. This can help surgeons decide whether a cancer can be removed and if so, it can help in planning the operation.

Angiography can be uncomfortable because the radiologist who does the procedure has to put a small catheter (a flexible hollow tube) into the artery leading to the liver to inject the dye. Usually the catheter is put into an artery in your inner thigh and threaded up into the liver artery. A local anesthetic is often used to numb the area before inserting the catheter. Then the dye is injected quickly to outline all the vessels while the x-rays are being taken.

Angiography may also be done with a CT scanner (CT angiography) or an MRI scanner (MR angiography). These techniques give information about the blood vessels in the liver without the need for a catheter, although you may still need an IV line so that a contrast dye can be injected into the bloodstream during the imaging.

Last Medical Review: 05/18/2009
Last Revised: 05/18/2009