The anus is the end of the large intestine. It is where stool (solid waste) leaves the body. The anus is formed partly from the outer skin layers of the body and partly from the intestine. The anus is connected to the rectum by the anal canal, which is about 1 to 1½ inches long. This area is controlled by two ring-like sphincter muscles, which contract to hold stool in and relax to allow its passage out of the body.
Anal cancer can start in the lining of the anal canal, called the mucosa, or in the perianal skin, the squamous cells outside of the anus that contain hair follicles and sweat glands.
Tumors of the perianal skin that do not involve the anal sphincter are usually treated the same as anal cancers, although local therapy (treatment directed to a limited area of skin) may be used for some.
Anal cancer is caused by certain changes to the way anal cells function, especially how they grow and divide into new cells. A risk factor is anything that increases the chance of getting a disease. Some risk factors for anal cancer can be changed. However, risk factors also include things people cannot change, like their genetics, getting older, and their health history.
There are many risk factors for anal cancer, but many do not directly cause cancer. Instead, they increase the chance of DNA damage in cells that may lead to anal cancer. To learn more about how cancer develops, see What Is Cancer?
Having one or more of these risk factors does not mean that you will get anal cancer. Many people with risk factors never develop anal cancer, while others with no known risk factors do.
Risk factors for anal cancer include:
Talk with your doctor if you think you may be at risk.
These and other signs and symptoms may be caused by anal cancer or by other conditions. Check with your doctor if you have:
In addition to asking about your personal and family health history and doing a physical exam, your doctor may perform the following tests and procedures:
The process used to find out if cancer has spread within the anus or to other parts of the body is called staging. The information gathered from this staging process determines the stage of the disease. It is important to know the stage in order to plan treatment. The following tests may be used in the staging process:
You may want to get a second opinion to confirm your anal cancer diagnosis and treatment plan. If you seek a second opinion, you will need to get medical test results and reports from the first doctor to share with the second doctor. The second doctor will review the pathology report, slides, and scans. They may agree with the first doctor, suggest changes or another treatment approach, or provide more information about your cancer.
Learn more about choosing a doctor and getting a second opinion at Finding Cancer Care. You can contact NCI’s Cancer Information Service via chat, email, or phone (both in English and Spanish) for help finding a doctor, hospital, or getting a second opinion. For questions you might want to ask at your appointments, visit Questions to Ask Your Doctor about Cancer.
The prognosis depends on:
The treatment options depend on:
Cancer stage describes the extent of cancer in the body, such as the size of the tumor, whether it has spread, and how far it has spread from where it first formed. It is important to know the stage of the anal cancer to plan the best treatment.
There are several staging systems for cancer that describe the extent of the cancer. Anal cancer staging usually uses the TNM staging system. The cancer may be described by this staging system in your pathology report. Based on the TNM results, a stage (I, II, III, or IV, also written as 1, 2, 3, or 4) is assigned to your cancer. When talking to you about your diagnosis, your doctor may describe the cancer as one of these stages.
Learn about tests to stage anal cancer. Learn more about Cancer Staging.
In stage 0, abnormal cells are found in the mucosa (innermost layer) of the anus. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called high-grade intraepithelial lesion (HSIL).
In stage I, cancer has formed and the tumor is 2 centimeters or smaller.
Stage II anal cancer is divided into stages IIA and IIB.
Stage III anal cancer is divided into stages IIIA, IIIB, and IIIC.
In stage IV, the tumor is any size. Cancer may have spread to lymph nodes or nearby organs and has spread to other parts of the body, such as the liver or lungs.
Stage IV anal cancer is also called metastatic anal cancer. Metastatic cancer happens when cancer cells travel through the lymphatic system or blood and form tumors in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor. For example, if anal cancer spreads to the liver, the cancer cells in the liver are actually anal cancer cells. The disease is called metastatic anal cancer, not liver cancer. Learn more in Metastatic Cancer: When Cancer Spreads.
Recurrent anal cancer is cancer that has come back after it has been treated. If anal cancer comes back, it may come back in the anus or in other parts of the body, such as the liver or lungs. Tests will be done to help determine where the cancer has returned. The type of treatment for recurrent anal cancer will depend on where it has come back.
Learn more in Recurrent Cancer: When Cancer Comes Back. Information to help you cope and talk with your health care team can be found in the booklet When Cancer Returns.
Different types of treatments are available for anal cancer. You and your cancer care team will work together to decide your treatment plan, which may include more than one type of treatment. Many factors will be considered, such as the stage of the cancer, your overall health, and your preferences. Your plan will include information about your cancer, the goals of treatment, your treatment options and the possible side effects, and the expected length of treatment.
Talking with your cancer care team before treatment begins about what to expect will be helpful. You’ll want to learn what you need to do before treatment begins, how you’ll feel while going through it, and what kind of help you will need. To learn more, visit Questions to Ask Your Doctor about Treatment.
Radiation therapy uses high-energy x-rays or other types of radiation to kill cancer cells or keep them from growing. There are two types of radiation therapy used to treat anal cancer:
Learn more about Radiation Therapy to Treat Cancer and Radiation Therapy Side Effects.
Chemotherapy (also called chemo) uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping the cells from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy).
Chemotherapy drugs used to treat anal cancer include:
Combinations of these drugs may be used. Other chemotherapy drugs not listed here may also be used.
Chemotherapy may be combined with other types of treatment, such as radiation therapy.
Learn more about how chemotherapy works, how it is given, common side effects, and more at Chemotherapy to Treat Cancer and Chemotherapy and You: Support for People With Cancer.
For some people, joining a clinical trial may be an option. There are different types of clinical trials for people with cancer. For example, a treatment trial tests new treatments or new ways of using current treatments. Supportive care and palliative care trials look at ways to improve quality of life, especially for those who have side effects from cancer and its treatment.
You can use the clinical trial search to find NCI-supported cancer clinical trials accepting participants. The search allows you to filter trials based on the type of cancer, your age, and where the trials are being done. Clinical trials supported by other organizations can be found on the ClinicalTrials.gov website.
Learn more about clinical trials, including how to find and join one, at Clinical Trials Information for Patients and Caregivers.
This summary section describes treatments that are being studied in clinical trials. It may not mention every new treatment being studied.
Radiosensitizers are drugs that make tumor cells more sensitive to radiation therapy. Combining radiation therapy with radiosensitizers may kill more tumor cells.
Immunotherapy helps a person’s immune system fight cancer. Your doctor may suggest biomarker tests to help predict your response to certain immunotherapy drugs. Learn more about Biomarker Testing for Cancer Treatment.
Immunotherapy drugs being studied in the treatment of anal cancer include:
Learn more about Immunotherapy to Treat Cancer.
For information about side effects caused by treatment for cancer, visit our Side Effects page.
As you go through treatment, you will have follow-up tests or check-ups. Some tests that were done to diagnose or stage the cancer may be repeated to see how well the treatment is working. Decisions about whether to continue, change, or stop treatment may be based on the results of these tests.
Some of the tests will continue to be done from time to time after treatment has ended. The results of these tests can show if your condition has changed or if the cancer has recurred (come back).
Treatment of stage 0 is usually local resection.
Learn more about this treatment in the Treatment Option Overview.
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
Treatment of stage I, stage II, and stage III anal cancer may include:
Those who have had treatment that saves the sphincter muscles may receive follow-up exams every 3 months for the first 2 years, including rectal exams with endoscopy and biopsy, as needed to check for recurrence.
Learn more about these treatments in the Treatment Option Overview.
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
Treatment of stage IV anal cancer may include:
Learn more about these treatments in the Treatment Option Overview.
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
In general, treatment for people who have anal cancer and HIV is similar to treatment for other people, and these patients have similar outcomes. However, this treatment can further damage the weakened immune systems of people who have HIV. Treatment for people with a history of AIDS-related complications may require lower doses of anticancer drugs and radiation therapy than doses used for patients who do not have HIV.
Treatment of recurrent anal cancer may include:
Learn more about these treatments in the Treatment Option Overview.
Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.
For more information from the National Cancer Institute about anal cancer, visit the Anal Cancer Home Page.
For general cancer information and other resources from the National Cancer Institute, visit:
Physician Data Query (PDQ) is the National Cancer Institute's (NCI's) comprehensive cancer information database. The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries come in two versions. The health professional versions have detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions have cancer information that is accurate and up to date and most versions are also available in Spanish.
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PDQ® Adult Treatment Editorial Board. PDQ Anal Cancer Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/anal/patient/anal-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389368]
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