Tests for Anal Cancer

Some people at high risk for anal cancer are diagnosed by screening tests, such as the digital rectal exam and/or anal Pap test (described in Can Anal Cancer Be Found Early?). Sometimes a doctor will find anal cancer during a routine physical exam or during a minor procedure, such as removing a hemorrhoid. Treating cancers found this way is often very effective because the tumors are found early in the course of the disease. (This means they're small and haven't spread.) But most often anal cancers are found because of signs or symptoms a person is having.

If anal cancer is suspected, exams and tests will be needed to confirm the diagnosis. If cancer is found, more tests will be done to help determine the extent (stage) of the cancer.

Medical history and physical exam

If you have symptoms that might be caused by anal cancer, the doctor will ask about your medical history to check for possible risk factors and learn more about your symptoms.

Your doctor will also examine you to look for signs of anal cancer or other health problems. For women, this will include a pelvic exam and Pap test. A digital rectal exam will probably be done, too. (This is when the doctor puts a gloved, lubricated finger into your anus and rectum to feel for lumps or other changes).

If problems or changes are found, your doctor might do other exams or tests to help find the cause. If you're being seen by your primary care doctor, you might be referred to a specialist such as a colorectal surgeon, also called a proctologist (a doctor specializing in diseases of the colon, rectum, and anus), for more tests and, if needed, treatment.


Endoscopy uses a thin tube with a lens or tiny video camera on the end to look inside part of the body. Many types of endoscopy can be used to look for the cause of anal symptoms. They can also be used to get tissue samples from inside the anal canal (described below under Biopsy). Drugs may be used to make you sleepy during these tests.


For anoscopy the doctor uses a short, hollow tube called an anoscope. It's 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 exam usually doesn't hurt.

Rigid proctosigmoidoscopy

The rigid proctosigmoidoscope is a lot like an anoscope, except that it's longer (about 10 inches long). It lets the doctor see the rectum and the lower part of the sigmoid colon. You might need to take laxatives or have an enema before this test to make sure your bowels are empty.


If a change or growth is seen during an endoscopic exam, your doctor will need to take out a piece of it to see if it's cancer. This is called a biopsy. If the growth is in the anal canal, this can often be done through the scope itself. Drugs may be used to numb the area before the biopsy is taken. Then, a small piece of the tissue is cut out and sent to a lab. If the tumor is very small, your doctor might try to remove the entire tumor during the biopsy.

A doctor called a pathologist will look at the tissue sample under a microscope. If cancer is present, the pathologist will send back a report describing the cell type and extent of the cancer.

Anal cancer sometimes spreads to nearby lymph nodes (bean-sized collections of immune system cells). Swollen lymph nodes in the groin can be a sign that cancer has spread. Lymph nodes may also become swollen from an infection. Biopsies may be needed to check for cancer spread to nearby lymph nodes.

There are many different ways to do a biopsy. A type called fine-needle aspiration (FNA) is often used to check lymph nodes that might have cancer in them. To do this, a small sample of fluid and tissue is taken out of the lymph node using a thin, hollow needle. A pathologist checks this fluid for cancer cells. If cancer is found in a lymph node, surgery may be done to remove the lymph nodes in that area.

Imaging tests

Imaging tests use x-rays, magnetic fields, sound waves, or radioactive substances to create pictures of the inside of your body. Imaging tests might be done for a number of reasons both before and after a diagnosis of anal cancer, including:

  • To help find cancer
  • To learn how far cancer has spread
  • To help see if treatment is working
  • To look for signs of cancer coming back after treatment

Some of these imaging tests are used more often than others.


Ultrasound uses sound waves to make pictures of internal organs or masses. This test can be used to see how deep the cancer has grown into the tissues near the anus.

For most ultrasound exams a wand-like transducer is moved around on the skin. But for anal cancer, the transducer is put right into the rectum. This is called a transrectal or endorectal ultrasound. The test can be uncomfortable, but it usually doesn't hurt.

Computed tomography (CT) scan

CT scans use x-rays to make detailed cross-sectional images of your body. This is a common test for people with anal cancer. It can be used to help tell if the cancer has spread into the lymph nodes or to other parts of the body, such as the liver, lungs, or other organs.

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.

CT-guided needle biopsy: CT scans can also be used to guide a biopsy needle right into a change that could be cancer. To do this, you stay on the CT scanning table while the doctor moves a biopsy needle through your skin and toward the tumor. CT scans are repeated until the needle is in the tumor. A biopsy sample is then taken out and sent to a lab to be looked at under a microscope.

Magnetic resonance imaging (MRI)

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 specific pattern formed by the type of tissue and by certain diseases. A computer translates the pattern into detailed images of parts of the body.

This test is sometimes used to see if nearby lymph nodes are enlarged, which might be a sign the cancer has spread there.

Chest x-ray

A regular x-ray might be done to find out if the cancer has spread to the lungs. It isn’t needed if a CT scan of the chest is done.

Positron emission tomography (PET) scan

For a PET scan, a form of radioactive sugar (known as fluorodeoxyglucose or FDG) is injected into your blood. Cancer cells are very active, so they absorb large amounts of the radioactive sugar. After about an hour, you'll be moved onto a table in the PET scanner. A special camera creates pictures of areas where the radioactivity has collected. The picture is not finely detailed like a CT or MRI scan, but it provides helpful information about your whole body.

Often a PET scan is done in a machine that can do a CT scan at the same time (a PET/CT scan). It lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed image of that area on the CT scan.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: November 13, 2017 Last Revised: November 13, 2017

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.