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. (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). Attention will also be focused on the groin area to see if any large lymph nodes are felt.  

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 or a gastroenterologist (doctors specializing in diseases of the colon, rectum, and anus) for more tests and, if needed, treatment.

Anoscopy

For anoscopy the doctor uses a short, hollow, firm 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 gel and then gently pushes it into the anus and lower rectum. By shining a light into this tube, the doctor has a clear view of the lining of the lower rectum and anus. Samples from abnormal areas (a biopsy) can be taken at the same time. You will be awake during this test, but it doesn't usually 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 anus, 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 so the doctor can see any abnormal areas clearly.

Endoscopy

Endoscopy uses a thin, flexible tube with a light and 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. A common type is a colonoscopy that can see the anus, rectum, and entire colon. It can also be used to get tissue samples from inside the anal canal, the rectum, and colon (described below under Biopsy). A flexible sigmoidoscopy might be done instead of a colonoscopy, but this only looks at the anal canal, rectum, and lower part of the colon. Drugs may be used to make you sleepy during these tests.

Biopsy

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 the 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 there is cancer, the pathologist will send back a report with the cell type and other details of the cancer, including whether it is related to an HPV infection.

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 tissue is taken out of the lymph node using a thin, hollow needle. A pathologist checks this tissue for cancer cells. If cancer is found in a lymph node, surgery may be done to remove the lymph nodes in that area.

Blood tests

HIV test: If you have risk factors for HIV, your doctor might order a blood test to check for it. This information is important because HIV positive patients might need to start treatment for HIV so that their immune system is as normal as possible, before starting cancer treatment.

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

Ultrasound

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 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. This test can 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.

CT-guided needle biopsy: A CT scan can also be used to guide a biopsy needle right into an area that could be cancer.

Magnetic resonance imaging (MRI)

MRI scans use radio waves and strong magnets instead of x-rays. A contrast material called gadolinium may be injected into a vein before the scan to see details better.

This test is sometimes used to see if nearby lymph nodes are enlarged, which might be a sign the cancer has spread there. MRI can also be used to look at abnormal areas in the liver or the brain and spinal cord that could be cancer spread. 

Chest x-ray

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

Positron emission tomography (PET) scan

For a PET scan, a slightly radioactive form of sugar (known as FDG) is injected into your blood. It collects mainly in cancer cells, which makes the cancer show up on the PET scan.

PET/CT scan: A CT scan can show more details than a PET scan, so a PET scan is often combined with a CT scan using a special machine that can do both at the same time. This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed image of that area on the CT scan.

PET/CT scans can be useful:

  • If your doctor thinks the cancer might have spread but doesn’t know where. They can show spread of cancer to the liver, bones, lymph nodes in the pelvis, or other organs. They are not as useful for looking at the brain or spinal cord.
  • In staging anal cancer when you are first diagnosed. But their role in checking whether treatment is working or after completion of treatment is unproven. Most doctors do not recommend PET/CT scans for routine follow up after anal cancer treatment, and most often will order CT or MRI scans to watch for cancer recurrence.

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.

Czito BG, Ahmed S, Kalady MF, and Eng C. Chapter 64: Cancer of the anal region. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg’s Cancer: Principles & Practice of Oncology. 11th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2019.

Goodman KA, Kachnic LA, Czito BG. Chapter 76: Cancer of the anal canal. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, Pa. Elsevier: 2020.

National Cancer Institute Physician Data Query (PDQ). Anal Cancer Treatment. 2020. Updated November 25, 2019. Accessed at https://www.cancer.gov/types/anal/patient/anal-treatment-pdq#_1 on March 26, 2020.

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Anal Carcinoma. V.1.2020. Accessed at www.nccn.org/professionals/physician_gls/pdf/anal.pdf on March 26, 2020.

Last Revised: September 9, 2020

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