Anal cancer: Full guide

What is anal cancer?

The anus is the opening at the end of the bowel where stool leaves the body. The anal canal is the short tube, about 1 to 2 inches long, that leads from the rectum to the outside. Anal cancer starts when cells in this area grow out of control.

Most anal cancers are caused by a common virus called human papillomavirus, or HPV. HPV spreads through skin contact during sex. Most people get HPV at some point, and the body usually clears it. When the virus stays for many years, it can slowly change cells, first into precancer and then into cancer. Having HPV is very common and nothing to be ashamed of.

Some people have a higher risk. This includes people living with HIV, people who have had an organ transplant or take medicines that weaken the immune system, people who have had cervical, vaginal, or vulvar cancer or precancer, and men who have sex with men. Smoking also raises the risk.

Common signs are bleeding from the bottom, pain or pressure in the anal area, itching, a lump near the anus, or a change in bowel habits. These are often blamed on hemorrhoids at first. If they do not go away, it is important to get checked.

Anal cancer is not the same as colon or rectal cancer. It is treated differently. Most people are treated with chemotherapy and radiation together, and many are cured without needing surgery that removes the anus.

Types and related conditions

Squamous cell carcinoma

By far the most common type, making up about 9 out of 10 anal cancers. It starts in the flat cells that line the anal canal. Almost all are linked to HPV. This guide is mostly about this type.

Anal canal cancer

Cancer inside the anal canal. It is usually treated with chemotherapy and radiation together.

Perianal (anal margin) cancer

Cancer in the skin just around the opening of the anus. Very small ones may be removed with surgery alone. Larger ones are treated like anal canal cancer.

Anal precancer (HSIL)

HSIL stands for high-grade squamous intraepithelial lesion. These are abnormal cells that are not cancer yet but could turn into cancer over time. Finding and treating them can lower the chance of cancer, especially in people living with HIV.

Adenocarcinoma of the anus

A rare type that starts in gland cells. It acts more like rectal cancer and is usually treated like rectal cancer.

Rare types

Melanoma and some other rare cancers can start in the anal area. They are treated very differently. Ask your care team to confirm your exact type.

Tests you may have

Physical and rectal exam

The doctor looks at the area and gently feels inside the anus and rectum with a gloved finger. Women also have a pelvic exam. The doctor feels the groin for swollen lymph nodes.

Anoscopy and high-resolution anoscopy

A short, lighted tube is placed in the anus to look at the lining. High-resolution anoscopy adds a magnifying scope to find small areas of precancer or cancer.

Biopsy

A small piece of tissue is taken and looked at under a microscope. This is the only way to know for sure that it is cancer and what type it is.

Lymph node biopsy

If a groin lymph node is swollen, a thin needle may take a sample to see if cancer has spread there.

Pelvic MRI

An MRI scan shows the size of the tumor and nearby lymph nodes. It helps plan radiation.

CT and PET-CT scans

These scans check the chest, belly, and pelvis for spread to lymph nodes, the liver, or the lungs. A PET-CT can also help plan radiation.

HIV test

Everyone with anal cancer should be offered an HIV test. Knowing your HIV status helps your care team plan safe treatment. People with HIV that is well controlled are treated the same way as others.

Blood tests

Blood counts and tests of your kidneys and liver make sure treatment is safe. People with HIV also have a CD4 count and viral load.

Gynecologic checkup

Because HPV can also affect the cervix, vagina, and vulva, women may be advised to have a Pap test or exam by a gynecologist.

What the stage means

The stage tells how big the tumor is and how far it has spread. Doctors use the TNM system. T is the size of the main tumor. N is whether cancer is in nearby lymph nodes. M is whether it has spread to distant parts of the body.

Anal cancer is grouped into stages 1 to 4. Most people are diagnosed at stage 1, 2, or 3, when the cancer is only in the anal area and nearby lymph nodes. These stages are treated with the goal of cure. Ask your care team to explain your stage.

Stage 1

A small tumor, 2 centimeters (about 3/4 inch) or less, that has not spread to lymph nodes.

Stage 2

A larger tumor that has not spread to lymph nodes.

Stage 3

The tumor has spread to nearby lymph nodes, or it has grown into nearby organs such as the vagina, bladder, or urethra.

Stage 4

The cancer has spread to distant parts of the body, such as the liver, lungs, or distant lymph nodes. Treatment aims to control the cancer and help you live longer and feel better.

Recurrent cancer

Cancer that comes back after treatment, in the anal area or elsewhere. There are still treatment options, including surgery for cancer that comes back only in the anal area.

Tumor markers and other tests

For anal cancer, treatment is mostly based on the stage and your overall health, not on gene tests. Some tests can still help your care team understand the cancer and plan care.

HPV and p16

A test on the biopsy can show if the cancer is linked to HPV. A protein called p16 is a sign of HPV. HPV-linked anal cancers tend to respond better to treatment.

HIV status and CD4 count

If you have HIV, your CD4 count (a measure of immune cells) and viral load help guide care. Keep taking your HIV medicines during cancer treatment, and make sure your HIV doctor and cancer team talk to each other.

PD-L1

A protein on some cancer cells. It may be tested if the cancer spreads. The approved immunotherapy for advanced anal cancer can be used whether or not the tumor has PD-L1.

Mismatch repair (MMR) or MSI

These tests look for a problem in how cancer cells fix their DNA. This is rare in anal cancer, but it may be checked if the cancer spreads, because it can point to immunotherapy options.

Tumor gene testing

If the cancer spreads, a larger gene test on the tumor may look for changes that could match a clinical trial.

Circulating tumor HPV DNA

A newer blood test that looks for bits of HPV DNA shed by the cancer. It is being studied to track how treatment is working. Ask your care team if it is right for you.

Main treatments

Chemoradiation

This is the main treatment for most anal cancers, and it is given with the goal of cure. Radiation is given 5 days a week for about 5 to 6 weeks. Chemotherapy is given during the same weeks to make the radiation work better. It lets most people keep the anus and normal bowel control.

Mitomycin and fluorouracil

The usual chemotherapy given with radiation is mitomycin plus fluorouracil (also called 5-FU). Fluorouracil is often given through a small pump you carry home. Some people take capecitabine pills instead of fluorouracil. Capecitabine turns into fluorouracil in the body.

Modern radiation (IMRT)

Intensity-modulated radiation therapy (IMRT) shapes the radiation beams to the tumor and lymph nodes. It helps spare the skin, bowel, bladder, and bone marrow, which lowers side effects.

Checking the response

Anal cancer can keep shrinking for months after treatment ends. Your care team usually checks with an exam about 8 to 12 weeks after treatment, then again over the next months. If the tumor is still shrinking, the team keeps watching. Many people who still have some tumor at the first check are clear by about 6 months, so surgery is not rushed.

Local surgery for very small tumors

Some very small cancers in the skin around the anus can be removed with surgery alone, if this can be done without harming the muscles that control the bowels.

Salvage surgery (abdominoperineal resection)

If cancer stays after chemoradiation or comes back in the anal area, surgery may be done to remove the anus and rectum. You would then have a permanent colostomy, where stool leaves the body through an opening in the belly into a bag. This surgery can still cure many people.

Chemotherapy plus immunotherapy for advanced cancer

For cancer that has spread or cannot be removed, the usual first treatment is carboplatin and paclitaxel chemotherapy. Adding the immunotherapy drug retifanlimab helps the cancer stay under control longer. This combination is FDA approved.

Immunotherapy after chemotherapy

If advanced cancer grows after chemotherapy, immunotherapy alone may be used. Retifanlimab is approved for this, and nivolumab or pembrolizumab are sometimes used. Other chemotherapy combinations are also options.

Treatment for people with HIV

People whose HIV is well controlled get the same treatment as others. Keep taking your HIV medicines. Your team will check for drug interactions.

Clinical trials

Research studies test new ways to treat anal cancer, such as lower radiation doses for small tumors or adding immunotherapy to chemoradiation. Ask if a trial is right for you.

Supportive (palliative) care

Care focused on comfort, symptoms, and quality of life. It can be given at any stage, along with cancer treatment.

Common side effects and what helps

Skin soreness from radiation

The skin around the anus, groin, and genitals often becomes red, sore, peeled, or raw, usually by the third or fourth week. Clean gently with warm water after using the toilet, and pat dry. Sitz baths (sitting in a few inches of warm water) can soothe. Wear loose cotton underwear. Use only creams your radiation team suggests. Tell your team about pain, because strong pain medicine is often needed for a few weeks.

Diarrhea and bowel urgency

Radiation to the pelvis and chemotherapy can cause loose stools and a strong need to go. Drink plenty of fluids. Anti-diarrhea medicine and a low-fiber diet can help. Call if you have 4 or more extra stools a day or feel dizzy.

Pain with bowel movements

Passing stool can hurt during and after treatment. Stool softeners, numbing creams, and pain medicine can help. Ask your team for a plan before pain gets bad.

Bladder irritation

You may have burning or need to pee often. Drinking water helps. Tell your team, because they may check for an infection.

Low blood counts

Mitomycin and fluorouracil can lower white cells, red cells, and platelets. Low white cells raise the risk of infection. Your team checks your blood often. Call right away for a fever.

Mouth sores and hand-foot changes

Fluorouracil and capecitabine can cause mouth sores, and capecitabine can make the palms and soles red and sore. Gentle mouth rinses and moisturizing creams help. Tell your team, because the dose may need to change.

Tiredness

Feeling very tired is common, and it often peaks near the end of radiation. Short walks and rest breaks help. It usually gets better in the weeks after treatment.

Tingling and hair loss from carboplatin and paclitaxel

Paclitaxel can cause numbness or tingling in the hands and feet, and hair loss. Report tingling early so the dose can be adjusted.

Immune side effects from immunotherapy

Immunotherapy can cause the immune system to attack healthy organs. This can cause diarrhea, cough, rash, or hormone problems like thyroid changes. Most are mild, but call your team about any new symptom.

Long-term changes

Some people have lasting bowel changes, such as urgency or leakage. Radiation can cause vaginal narrowing and dryness, erection problems, and weaker pelvic bones. It can also cause early menopause and loss of fertility. Ask about fertility options before treatment. Pelvic floor therapy, vaginal dilators, and other treatments can help.

Living with and after anal cancer

After treatment, you will have regular checkups with an exam of the anal area and groin, often every few months for the first few years. You may also have anoscopy and scans. Most cancers that come back do so in the first 3 years.

Bowel habits may take months to settle. Some people have lasting urgency or leakage. A pelvic floor physical therapist, diet changes, and medicines can help. Tell your care team, because there is a lot that can be done.

Treatment can change your sex life and how you feel about your body. For women, using a vaginal dilator after radiation helps prevent narrowing. Men may have erection problems that can be treated. It is okay to bring these topics up with your team.

If you smoke, quitting helps treatment work better and helps you heal. If you have HIV, keep taking your HIV medicines and see your HIV doctor regularly.

Screening helps people at high risk. Experts now advise regular anal cancer screening for people living with HIV (starting around age 35 for men who have sex with men and transgender women, and around 45 for others), people who have had an organ transplant, and women who have had vulvar cancer or precancer. Screening may use a swab test, an exam, and high-resolution anoscopy. Ask your doctor if you should be screened.

The HPV vaccine can prevent most anal cancers. It works best when given before any contact with HPV, but adults up to age 45 can talk with their doctor about it. Encourage your children and grandchildren to get it. It is normal to feel worried, sad, or embarrassed. Support groups and counselors can help, and no one deserves cancer.