Anal Cancer

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Early Detection, Diagnosis, and Staging TOPICS

How is anal cancer diagnosed?

Anal cancer is often fairly easy to diagnose because it is in a fairly easy-to-reach area. Some cases of anal cancer in people at high risk for that disease are diagnosed by screening tests, such as the digital rectal exam and/or anal Pap test, but most people are diagnosed after their cancer starts to cause symptoms.

Signs and symptoms of anal cancer

Some cases of anal cancer cause no symptoms at all. In more than half of patients, bleeding occurs and is often the first sign of the disease. The bleeding is usually minor. At first, most people assume that hemorrhoids are the cause of their bleeding. Hemorrhoids are painful, swollen veins in the anus and rectum that may bleed. They are a benign and fairly common cause of rectal bleeding.

Itching can also be a symptom. This is more often a sign of AIN, which may also need to be treated. Important symptoms of anal cancer include:

  • Rectal bleeding
  • Rectal itching
  • Pain in the anal area
  • Change in the diameter of stool
  • Abnormal discharge from the anus
  • Swollen lymph nodes in the anal or groin areas

There are a number of benign conditions, like hemorrhoids, fissures, fistulas, and anal warts that can cause similar symptoms. But if any of the signs or symptoms of anal cancer are present, discuss them with your doctor without delay. Remember, the sooner you receive a correct diagnosis, the sooner you can start treatment, and the more effective your treatment will be.

Procedures used to diagnose anal cancer

Sometimes a doctor will detect anal cancer during a routine physical exam or during a minor procedure, such as removing a hemorrhoid. Treating cancers found in this way is often very effective because the tumors are found early in the course of the disease.

An unusual growth may also be found on a digital rectal exam. But since doctors cannot see what they feel, other steps may be needed if you have symptoms or if your doctor suspects you have anal cancer.


Endoscopy is the use of a tube with a lens or video camera on the end to examine an inner part of the body. Several types of endoscopy may be used to look for the cause of anal symptoms. For these tests you either lie on your side on top of an examining table, with your knees bent up to your chest, or you bend forward over the table. Types of endoscopy include:

Anoscopy: Anoscopy uses a short, hollow tube (an anoscope), which is 3 to 4 inches long and about 1 inch in diameter, and may have a light on the end of it. The doctor coats the anoscope with a lubricant and then gently pushes it into the anus and rectum. By shining a light into this tube, the doctor has a clear view of the lining of the lower rectum and anus. This is usually not painful.

Rigid proctosigmoidoscopy: The rigid proctosigmoidoscope is similar to an anoscope, except that the proctoscope is 10 inches long, so it allows the doctor to view the rectum as well as the lower part of the sigmoid colon. This test usually requires that you take laxatives or have an enema beforehand to make sure the bowels are empty.


If a suspicious growth is found, your doctor will need to take a sample of tissue to see if it is cancer. This is called a biopsy. This can often be done through the scope itself. You may get a local anesthetic to numb the area before the biopsy is taken. Then, a small piece of the tissue is cut out and sent to a lab.

A pathologist (a doctor specializing in lab diagnosis of diseases) will look at the sample under a microscope. If cancer is present, the pathologist will send back a report describing the cell type and extent of the cancer.

If the tumor is very small and has not grown below the surface of the anus into other tissues, your doctor may attempt to remove the entire tumor during the biopsy.

Other types of biopsy may be used to check for cancer spread to lymph nodes, such as:

Fine-needle aspiration biopsy: Anal cancer sometimes spreads through the lymphatic system to lymph nodes. Lymph nodes are bean-sized collections of immune system cells. Swollen lymph nodes in the groin can be a sign of spreading anal cancer. Lymph nodes may also become swollen from an infection. To see if cancer is causing an enlarged lymph node, your doctor may withdraw a small sample of fluid and tissue from the lymph node with a thin needle. The lab will study this fluid to look for the presence of cancer cells. This procedure is called a fine-needle aspiration biopsy. If cancer is found in a lymph node, an operation to remove the lymph nodes in that area may then be done.

Sentinel node biopsy: This test is sometimes used to help determine if cancer that has already been diagnosed has spread to the lymph nodes. In this test a low-level radioactive tracer material is injected around the tumor. Often a blue dye is injected into the tumor at the same time. The groin lymph nodes are scanned to see where the radioactive material has traveled. The doctor removes any radioactive or blue-stained lymph nodes. A pathologist then looks at the nodes for evidence of cancer cells. This helps tell how far the cancer may have spread, because these nodes would be the ones that any cancer cells leaving the tumor would have spread to first. While this test has been shown to be useful for some other cancers, it's not yet clear how helpful it is for anal cancer.

Imaging studies

If cancer is found, you may have certain tests to see how far it has spread. Some of these tests are used more often than others.


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 high-frequency sound waves. These sound waves pass into the area of the body being studied and are echoed back. The echoes are picked up by the transducer and converted by a computer into an image on a screen. Ultrasounds are very safe and use no radiation.

For most ultrasound exams the transducer is placed on the skin to take pictures of internal organs. For anal cancer, though, the transducer is inserted directly into the rectum. This is known as transrectal or endorectal ultrasound. The test can be slightly uncomfortable, but it usually is not painful. It is used to see how deep the cancer has grown into the tissues surrounding the anus.

Computed tomography (CT) scan

The computed tomography (CT) scan is an x-ray test that produces detailed cross-sectional images of your body. Instead of taking one picture, like a standard x-ray, a CT scanner takes many pictures as it rotates around you. A computer then combines these into an image of a slice of your body. A CT scan can be used to tell if the anal cancer has spread into the liver or other organs.

A CT scanner has been described as a large donut, with a narrow table in the middle opening. You will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken.

Before the test, you may be asked to drink 1 to 2 pints of a liquid called oral contrast. This helps outline the intestine so that certain areas are not mistaken for tumors. You may also receive an IV line through which a different kind of contrast dye (IV contrast) is injected. This helps better outline structures such as blood vessels in your body.

The injection can cause some flushing (redness and warm feeling). A few people are allergic to the dye and get hives, or rarely, have 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-guided needle biopsy: CT scans can also be used to guide a biopsy needle precisely into a suspected tumor. For this procedure, the patient remains on the CT scanning table, while a doctor advances a biopsy needle through the skin and toward the tumor. CT scans are repeated until the needle is within the mass. A fine-needle biopsy sample or a larger core-needle biopsy sample is then removed and looked at under a microscope.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) scans use radio waves and strong magnets instead of x-rays to make images of the body. The energy from the radio waves is absorbed by the body and then released in a specific pattern formed by the type of tissue and by certain diseases. A computer translates the pattern into a detailed image of parts of the body. Like a CT scanner, this produces cross-sectional slices of the body. An MRI can produce slices that are parallel with the length of your body. As with a CT scan, a contrast material might be used, but it is not needed as often.

MRI scans are more uncomfortable than CT scans. They take longer -- often up to an hour. You have to be placed inside tube-like equipment. This is confining and can upset people that suffer from claustrophobia (a fear of enclosed spaces). If you have trouble with close spaces, let your doctor know before the MRI scan. Sometimes medication can be given just before the scan to reduce anxiety. Another option is to use a special "open" MRI machine that is less confining and more comfortable for such people. The MRI machine makes a buzzing or clanging noise that some people may find disturbing. Some places will provide headphones with music to block this sound.

Chest x-ray

This test may be done to find out whether anal cancer has spread to the lungs.

Positron emission tomography (PET)

PET scans use glucose (a form of sugar) that contains a low-level radioactive atom. Because they are very active, cancer cells in the body absorb larger amounts of the sugar than normal cells and display more radioactivity. A special camera can be used to detect this radioactivity. PET is useful when your doctor thinks the cancer has spread, but doesn't know where. Often a PET scan is done in a machine that can do a CT scan at the same time. This is called a PET/CT scan.

Last Medical Review: 01/02/2013
Last Revised: 01/02/2013