Anal Cancer Overview

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Early Detection, Diagnosis, and Staging TOPICS

How is anal cancer found?

Many cases of anal cancer can be found early. Anal cancers form in a part of the body that the doctor can see and reach easily. Sometimes anal cancer does not cause any symptoms at all. But a rectal exam will still find some cases early. For this exam (called a DRE), the doctor puts a gloved finger into the anus to feel for lumps or growths. A rectal exam may be used to check for prostate cancer in men. For women, the rectal exam is done as part of the pelvic exam. If you are at higher risk for anal cancer, ask your doctor if you should have this exam (or any other tests) more often.

Doctors can also test people at high risk for sexually transmitted diseases with a test called an anal Pap. It is much like the Pap smear done for cervical cancer. The anal lining is swabbed and the cells are looked at under a microscope. Some doctors think that this test should be done routinely for people at high risk for anal cancer. That would include men who have sex with men, women who have had cervical cancer or vulvar cancer, all HIV-positive men and women, and all transplant patients. People with positive results should be referred for a biopsy and, depending on the results, treated. Still, not all doctors believe this test is helpful, because no study has shown that it lowers the chance of getting invasive anal cancer.

Signs and symptoms of anal cancer

Some cases of anal cancer have no symptoms at all. But people who do have symptoms of anal cancer may notice one or more of the following:

  • Bleeding or itching around the anus
  • Pain in the anal area
  • Change in the width of the stool (stool may be narrower than usual)
  • Swollen lymph nodes in the anal or groin area
  • Abnormal discharge from the anus

Itching can also be a symptom. This is more often a sign of anal pre-cancer, which may also need to be treated.

These symptoms can also be caused by something other than cancer, but only your doctor can tell for sure. Talk to your doctor right away if you notice any of these problems.

Tests for anal cancer

The doctor may feel a growth during a rectal exam. But since doctors cannot see what they feel, other steps may be needed if you have symptoms or if your doctor thinks you may have anal cancer.


Endoscopy is the use of a tube with a lens or video camera on the end (called a scope) to look inside the body. Endoscopy may be used to look for the cause of anal symptoms.

Anoscopy: For this test you either lie on your side on top of an exam table, with your knees bent up to your chest, or you bend forward over the table. The doctor coats the anoscope (which is about 4 inches long) 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 and sometimes the lower part of the colon. 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 see the rectum as well as the lower part of the colon. You will most likely need to take laxatives or have an enema before the test to make sure the bowels are empty.


In order to find out if a growth is cancer, a biopsy must be done. For a biopsy, the doctor will remove a sample of tissue and send it to a lab to be looked at under a microscope. For anal cancer, this tissue sample is most often removed during endoscopy. If the tumor is very small and has not grown below the surface of the anus, your doctor may be able to take out the whole tumor during the biopsy.

Other types of biopsies that may be done to look for cancer spread to the lymph nodes include:

Fine-needle aspiration biopsy

Since anal cancer can spread through the lymph system, your doctor may want to do a biopsy of your lymph nodes, too. Lymph nodes are bean-sized groups of immune system cells. Swollen lymph nodes are sometimes a sign of spreading cancer. Most often, though, they are a sign of infection. A small (fine) needle is placed into the swollen node. It is used to remove some cells and fluid that is then sent to the lab. In some cases, an operation to remove the lymph nodes near the anus may be done.

Sentinel node biopsy

In this test, a needle is used to put a radioactive substance, often with a blue dye, into the tumor. The dye moves into the nodes that carry fluid away from the tumor. 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. The surgeon then takes out any blue-stained nodes and looks at them to see if they contain cancer cells. 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 tests

If cancer is found, you may have tests to see how far it has spread. These tests produce different kinds of pictures of the inside of the body. Some of these tests are used more often than others.


Ultrasound uses sound waves to make a picture of the inside of the body. Most people know about ultrasound because it is often used to look at a baby during pregnancy. For anal cancer, a probe must be placed in the rectum, which can be slightly uncomfortable but should not be painful. This test can show how far the cancer might have grown into nearby tissues.

CT scan (computed tomography)

A CT scan can help tell whether anal cancer has spread to the liver or other organs. The CT scan machine moves around you and uses x-rays to take many pictures of the body. A computer then combines them to make pictures of cross-sections of the body.

A CT scanner has been described as a large donut, with a narrow table in the middle “hole”. 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.

You may be asked to drink 1 to 2 pints of a liquid called oral contrast which helps to outline the intestine on the pictures. You may also have a contrast “dye” put into a vein. When it is injected, you may feel warm and your skin may become red. Some people are allergic and get hives or, rarely, more serious problems such as 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 can also be used to guide a biopsy needle into a tumor.

MRI (magnetic resonance imaging)

Like CT scans, MRI scans show a cross-section of the body but in more detail. MRI uses radio waves and strong magnets instead of x-rays to take pictures. They take longer and you have to lie inside a tube-like machine, which can be upsetting for some people. If you have trouble with closed spaces, let your doctor know before the MRI scan. Sometimes drugs can be given just before the scan to help you relax. Another option is to use special “open” MRI machines where you will feel less closed in.

MRI machines also make loud thumping noises that can be distracting. Some places offer earplugs with music to help reduce the noise of the machine.

Chest x-rays

These may be done to see whether the anal cancer has spread to the lungs.

PET scan (positron emission tomography)

This test uses sugar combined with a radioactive atom that is put into a vein. Cancer cells absorb high amounts of the sugar and a special camera is used to see to show these areas. PET scans look for cancer in the whole body. They are useful when the doctor thinks the cancer has spread but doesn’t know where. There are machines that do a PET and CT scan at the same time.

Last Medical Review: 01/14/2013
Last Revised: 01/17/2013