Anal Cancer Screening: Tests, Guidelines, and Prevention

What Is Anal Cancer Screening?

Anal cancer screening is a way for doctors to check the anus for early signs of cancer before a person has any symptoms. The anus is the short tube at the end of the digestive system where stool leaves the body. Screening tests look for abnormal cell changes, called precancer, that can turn into cancer over time if they are not treated. Finding these changes early gives doctors a chance to treat them before cancer ever develops.

Unlike breast cancer or colorectal cancer, there is no single national screening program for anal cancer in the United States. Groups like the U.S. Preventive Services Task Force have not issued a general population recommendation for anal cancer screening the way they have for cervical or colon cancer. This means most healthy adults with average risk are not routinely screened for anal cancer.

However, this does not mean screening is unimportant. Certain groups of people face a much higher chance of developing anal cancer, and medical experts strongly encourage screening for these groups. According to the American Cancer Society, about 11,270 people in the United States are expected to be diagnosed with anal cancer this year, and about 1,700 people are expected to die from it. While these numbers are much smaller than for many other cancers, the rate of anal cancer has been rising for decades, especially among certain high-risk groups.

The main cause of anal cancer is human papillomavirus, often called HPV. This is the same virus responsible for most cervical cancers. The National Cancer Institute reports that HPV is found in roughly 90 percent of anal cancers. Because HPV spreads through skin-to-skin contact during sexual activity, people with certain sexual histories and weakened immune systems face a higher chance of long-term HPV infection turning into precancer.

Screening for anal cancer usually focuses on finding a condition called anal high-grade squamous intraepithelial lesion, often shortened to HSIL. This is the medical term for precancerous cell changes in the lining of the anal canal. If HSIL is left untreated, it can slowly progress into invasive anal cancer over a period of years. Screening tools are designed to catch HSIL, or even anal cancer itself, at the earliest and most treatable stage.

A landmark study called the ANCHOR trial, funded by the National Institutes of Health, changed the conversation around anal cancer screening. This study followed thousands of people living with HIV and found that treating HSIL lowered the risk of developing anal cancer by 57 percent compared with simply watching and waiting. This is strong proof that screening and early treatment can actually save lives, not just find problems earlier.

Because of results like the ANCHOR trial, medical organizations have published detailed screening guidance for people living with HIV. These groups agree that screening should be a normal part of care for people at high risk, even though a broad national program for the general public does not yet exist.

It helps to think of anal cancer screening the same way many people already think about cervical cancer screening. Just as a Pap test looks for abnormal cervical cells before they become cancer, an anal Pap test looks for abnormal anal cells. The goal in both cases is the same: catch problems early, treat them, and prevent cancer from ever forming.

Types of Anal Cancer Screening Tests

There are three main tests doctors use to screen for anal cancer and anal precancer. Understanding what each one involves can help you feel more prepared and less anxious if your doctor recommends screening.

• Digital rectal exam, sometimes called a DRE. During this exam, a doctor puts on a lubricated glove and gently inserts a finger into the anus and lower rectum to feel for lumps, thickened areas, or other abnormalities. This exam takes only a minute or two and can often be done as part of a routine physical checkup. While a digital rectal exam cannot detect early precancer cells, it is a useful and low-cost way to catch tumors or masses that might otherwise go unnoticed.

• Anal cytology, though most people know it as an anal Pap smear. This test works almost exactly like the cervical Pap test that many women already receive. The doctor or nurse gently inserts a small swab, similar to a cotton swab, into the anal canal and rotates it to collect cells from the lining. Those cells are sent to a laboratory, where a specialist examines them under a microscope for abnormal changes. The test itself takes only a few minutes and does not usually require any special preparation.

  An anal Pap smear can sometimes be paired with HPV testing on the same sample. This checks whether high-risk strains of HPV, like HPV 16 or HPV 18, are present. According to the HIV clinical guidelines program, doctors may use cytology alone, HPV testing alone, or a combination of both, depending on what is available and what a patient's individual risk level looks like.

• High-resolution anoscopy, often shortened to HRA. This procedure is similar in concept to a colposcopy, which is the follow-up test many women receive after an abnormal cervical Pap smear. During high resolution anoscopy, a doctor uses a special magnifying instrument called a colposcope to closely examine the lining of the anal canal. The doctor applies a vinegar-like solution, and sometimes an iodine solution, to the tissue, which helps abnormal areas show up more clearly.

  High-resolution anoscopy allows the doctor to see precancerous changes that would be completely invisible to the naked eye. If an abnormal area is found, the doctor can take a small tissue sample, called a biopsy, right then and there. This sample is sent to a lab to confirm whether the cells show HSIL, a lower grade change, or nothing concerning at all. Many patients describe the procedure as similar to a rectal exam with mild pressure, and it is usually done in an outpatient office setting without general anesthesia.

• Sigmoidoscopy: The sigmoidoscope is a lot like an anoscope, except 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.

• Colonoscopy: A colonoscopy allows the doctor to see the anus, rectum, and entire colon. It can be used to get tissue samples from inside the anal canal, the rectum, and colon (described below under Biopsy).  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  pathologist will look at the tissue sample with 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. 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.

• Complete blood count (CBC): This test measures the different types of cells in your blood. It can show if you have anemia (too few red blood cells). Some people with anal cancer become anemic because the tumor has been bleeding for a long time.

• Liver enzymes: You may also have a blood test to check your liver function, because anal cancer can spread to the liver.

• HIV test: If you have been diagnosed with anal cancer, specifically squamous cell anal cancer, your doctor may check your HIV status with a blood test. This information is important because HIV-positive patients might need to start treatment for HIV 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 may be done for a number of reasons, such as:

• To look at suspicious areas that might be cancer

• To learn how far cancer might have spread

• To help determine if treatment is working

• To look for signs of cancer coming back after treatment

Ultrasound

Ultrasound uses sound waves and their echoes to create images of the inside of the body. A small microphone-like instrument called a transducer gives off sound waves and picks up the echoes as they bounce off organs. The echoes are converted by a computer into an image on a screen.

Endorectal ultrasound

A special transducer is put into the rectum to see how far through the rectal wall a cancer has grown and if it has reached nearby organs or lymph nodes.

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.

Magnetic resonance imaging (MRI)

Like CT scans, MRI scans show detailed images of soft tissues in the body. But 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 get clear pictures.  MRI can be used to look at abnormal areas in the liver or the brain and spinal cord that could be cancer spread.

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.

Researchers continue to study newer testing methods, including different HPV DNA tests and biomarker tests that might one day make screening more precise. For now, the combination of digital rectal exams, anal cytology, and high-resolution anoscopy for follow-up remains the standard approach.

When Should You Start Screening for Anal Cancer?

Since there is no single national guideline for the general public, the right age to start anal cancer screening depends heavily on your personal risk factors. Doctors look closely at your health history, including HIV status, sexual history, and any past cancers, to figure out the right plan for you.

People living with HIV are considered the highest priority group for anal cancer screening. This is because HIV weakens the immune system's ability to clear HPV infections on its own, allowing the virus to linger and cause cell damage over many years. Screening is recommended starting at age 35 for men who have sex with men living with HIV, transgender women living with HIV, and transgender men who have had sex with men and are living with HIV.

For other people living with HIV, including cisgender women and heterosexual men, screening is recommended starting at age 45 under these same guidelines. The guidelines also note something important: anal precancer and cancer can develop even without a history of anal sex, so all people living with HIV should be considered for screening once they reach the recommended age.

Men who have sex with men who do not have HIV also face a higher than average risk, according to the American Cancer Society. While formal age guidance is less settled for this group compared with people living with HIV, many specialists suggest starting conversations about screening in a person's thirties or forties, especially if additional risk factors are present.

Women with a history of cervical, vaginal, or vulvar precancer or cancer make up another important high-risk group. This is because these conditions share the same underlying cause, persistent HPV infection, and the virus can affect more than one area of the body. The American Cancer Society specifically highlights women over the age of 45 who test positive for HPV 16 as a group that should discuss screening with their doctor.

People who have received an organ transplant are also at higher risk because they take medications that suppress the immune system to prevent organ rejection. This immune suppression makes it harder for the body to control HPV infection, similar to what happens with HIV. The same is true for people who take long-term immunosuppressive medications for autoimmune diseases such as lupus, rheumatoid arthritis, or inflammatory bowel disease.

A history of receptive anal intercourse, regardless of gender or HIV status, raises the chance of HPV exposure in the anal canal and is another factor doctors consider. A history of genital warts, which are also caused by HPV, is another signal that a doctor might discuss screening with a patient.

The bottom line is that there is no single universal starting age that applies to everyone. Instead, doctors calculate an individualized risk profile based on HIV status, sexual history, immune health, and past HPV related diagnoses. If you fall into one or more of the high-risk categories described above, the most important step is simply to bring it up with your primary care doctor, gynecologist, or HIV care provider so they can help you decide when to begin.

Which Screening Tests Should I Choose?

Choosing the right combination of screening tests is not a decision you need to make alone. This is truly a conversation to have with your doctor, who can weigh your personal risk factors, local resources, and personal comfort level. That said, understanding the general approach that experts recommend can help you ask better questions at your next appointment.

For most high-risk patients, especially people living with HIV, the recommended starting point is an annual visit that includes a symptom check, a visual inspection of the area around the anus, and a digital rectal exam. This exam should always be performed before any cell sample is collected, since lubricant and manipulation of the tissue can interfere with the accuracy of a Pap test done afterward.

Annual anal cytology, the anal Pap smear, is typically the next layer of screening added for high-risk patients. Some clinics choose to combine this test with HPV testing on the same sample, since knowing whether high-risk HPV strains are present can help guide how closely a patient needs to be followed. The right choice between cytology alone, HPV testing alone, or a combined approach often depends on what your particular clinic offers and what insurance will cover.

If your anal Pap smear or HPV test comes back abnormal, your doctor will likely refer you for high-resolution anoscopy. This is considered the gold standard follow-up test because it allows direct visualization and biopsy of suspicious tissue. Because this procedure requires specialized training, you may need a referral to a colorectal surgery clinic, an academic medical center, or an HIV specialty clinic that offers this service.

The results of the ANCHOR trial have strengthened the case for this full screening pathway, cytology followed by high-resolution anoscopy when needed, particularly for people living with HIV who are age 35 and older. Because the study proved that treating HSIL reduces cancer risk by more than half, many experts now consider this combination of tests to be standard care rather than optional extra care for this group.

If your test results are normal, your doctor will usually recommend repeating screening every year, since HPV related cell changes can develop over time even after a clear result. Some guidelines allow for less frequent screening, such as every three years, for people who have had two consecutive clear results for both HPV and cell abnormalities, but this decision should always be made with your doctor rather than on your own.

If you do not fall into one of the higher risk categories described earlier, it is still worth mentioning any symptoms you notice, such as unexplained bleeding, itching, pain, or a new lump near the anus, to your doctor right away. Even without routine screening, paying attention to your body and reporting changes quickly is one of the best tools you have for catching problems early.

Because guidelines continue to evolve as more research becomes available, it is a good idea to check in with your doctor periodically about whether new recommendations apply to you.

Reducing Your Risk of Anal Cancer Through Lifestyle Changes

While screening helps catch problems early, there are also steps you can take to lower your actual chance of developing anal cancer in the first place. The most effective tool available today is the HPV vaccine. This vaccine protects against the strains of HPV most likely to cause cancer, including anal cancer. The Centers for Disease Control and Prevention recommends that children receive the vaccine starting at age 11 or 12, though it can be given as early as age 9 and is approved for adults through age 26. Some adults between the ages of 27 and 45 may also benefit from vaccination after talking with their doctor.

• Quitting smoking is another powerful way to lower your risk. According to the National Cancer Institute, current smokers face two to three times the risk of anal cancer compared with people who have never smoked. If you smoke, talk with your doctor about resources like nicotine replacement therapy or counseling programs. Many free resources are available through CDC's Tips From Former Smokers program and the national quitline at 1-800-QUIT-NOW.

• Practicing safer sex is another meaningful step. Using condoms and dental dams can reduce, though not completely eliminate, the spread of HPV and HIV. Limiting the number of sexual partners and having open conversations with partners about sexual health history can also help lower your overall exposure to HPV over your lifetime.

• If you are living with HIV, staying consistent with antiretroviral therapy is important for more reasons than immune health alone. Keeping your immune system as strong as possible may help your body better control HPV infections and reduce the chance that cell changes will progress to precancer. Talk with your HIV care team about how your treatment plan connects to your overall cancer prevention strategy.

• Maintaining regular medical care overall, rather than only visiting a doctor when something feels wrong, gives you more opportunities to catch and manage risk factors early. This includes keeping up with routine bloodwork, staying current on other recommended vaccines, and mentioning any new or unusual symptoms as soon as they appear rather than waiting.

• If you take medications that suppress your immune system, such as after an organ transplant or for an autoimmune condition, work closely with both your specialist and your primary care doctor. These providers should be aware of your increased cancer risk so that screening and monitoring can be built into your regular care plan rather than treated as an afterthought.

• Diet and general health habits, while not proven to directly prevent anal cancer the way they help with some other cancers, still support a stronger immune system overall. Eating a balanced diet, staying physically active, and managing chronic conditions like diabetes can all contribute to better overall immune function, which may help your body fight off persistent HPV infection.

Finally, remember that reducing risk is not about achieving perfection. Even small, sustainable changes such as quitting smoking, staying up to date on vaccines, or scheduling that first screening appointment can make a real difference over time. Combining these lifestyle steps with appropriate screening, especially for those in high-risk groups, gives you the strongest possible protection against anal cancer.

Sources:

• Anal Cancer Screening, Detection and Diagnosis - American Cancer Society

• In People with HIV, Treating Precancerous Anal Lesions Cuts Risk of Anal Cancer by More Than Half - National Institutes of Health

• Update on Clinical Guidelines for High Resolution Anoscopy and Anal Cancer Screening, NIH Office of AIDS Research

• Human Papillomavirus (HPV) Vaccination - Centers for Disease Control and Prevention

• Cancers Caused by HPV - Centers for Disease Control and Prevention

• Anal Cancer - MedlinePlus, National Library of Medicine