Page last updated: July 2024
The information on this webpage was adapted from Understanding Anal Cancer - A guide for people affected by cancer (2024 edition). This webpage was last updated in July 2024.
Expert content reviewers:
This information was developed with the help of a range of health professionals and people affected by anal cancer:
- Dr Glen Guerra, Colorectal Surgeon, Peter MacCallum Cancer Centre and St Vincents Hospital Melbourne, VIC
- Holly Davey, 13 11 20 Consultant, Cancer Council Queensland
- Prof Peter Gibbs, Laboratory Head, Walter and Eliza Hall Institute, The University of Melbourne, Medical Oncologist, Western Hospital, VIC
- A/Prof Ian Faragher, The University of Melbourne, Head of Colorectal and General Surgery Unit, Western Health, VIC
- Justin Hargreaves, Medical Oncology Nurse Practitioner, Bendigo Health Cancer Centre, VIC
- Prof Richard Hillman, Senior Staff Specialist, HIV and Immunology, St Vincent’s Health Network, Sydney, Conjoint Professor, St Vincent’s Clinical Campus and The Kirby Institute, NSW
- A/Prof George Hruby, Radiation Oncologist, Royal North Shore Hospital, Visiting Radiation Oncologist, Genesiscare and Dubbo Base Hospital, NSW
- Annie Jacobs, Consumer
- Mariad O’Gorman, Clinical Psychologist, Bankstown Cancer Therapy Centre, NSW
- Terry Scully, Consumer
About the anus
The anus is the opening at the end of the large bowel. It is made up of the last few centimetres of the bowel (anal canal) and the skin around the opening (anal margin).
During a bowel movement, the anus muscles (sphincters) relax to release the solid waste matter known as faeces, stools or poo.
What is anal cancer?
Anal cancer affects the tissues of the anus. It can start in any part of the anus including the anal margin, anal canal and transitional zone.
Cancer is a disease of the cells, the body’s basic building blocks which make up tissues and organs. The body constantly makes new cells to help us grow, replace worn-out tissue and heal injuries.
Normally, cells multiply and die in an orderly way, with each new cell replacing one lost. Sometimes cells become abnormal and keep growing. These abnormal cells may form a lump or tumour.
If the cells in a tumour are cancerous, they can spread through the bloodstream or lymph vessels and form another tumour at a new site. This new tumour is known as secondary cancer or metastasis.
Types of anal cancer
Squamous cell carcinoma (SCC)
Most anal cancers are SCCs. These start in the flat (squamous) cells that line much of the anus. The term “anal cancer” commonly refers to SCCs, and this page focuses on this type of anal cancer.
Adenocarcinoma
This is a less common type of anal cancer. Adenocarcinomas can start in cells that line the upper part of the anus near the rectum or in the glands that release secretions into the anal canal. It can be treated in a similar way to bowel cancer.
Skin cancer
In rare cases, SCCs can affect the skin just outside the anus. These are called anal margin SCCs. If they are not too close to the sphincter muscles, they can be treated in a similar way to SCCs on other areas of the skin.
How common is anal cancer?
Every year, about 615 people are diagnosed with anal cancer in Australia. It is more common over the age of 50 and more women than men are diagnosed with it.
The number of people diagnosed with anal cancer has increased over recent decades.
While anal cancer is rare (fewer than two cases in 100,000 people), rates are more than 40 times higher in gay and bisexual men and other men who have sex with men.
See LGBTQI+ People and Cancer or visit The Bottom Line for specific information.
Risk factors
About 90% of anal cancer cases are caused by infection with specific strains of a very common virus called human papillomavirus (HPV).
HPV can infect the surface of different areas, including the anus, cervix, vulva, vagina, penis, mouth and throat. Some HPV strains cause anal and genital warts.
About 4 out of 5 people will become infected with one type of genital HPV at some time in their lives. Unless they are tested, most people won’t know they have an HPV infection as it usually doesn’t cause symptoms.
If cancer develops, it usually appears many years after the first infection. Other risk factors for anal cancer include:
- having a weakened immune system, for example because of human immunodeficiency virus (HIV) infection, an organ transplant or an autoimmune disease such as coeliac disease, lupus or Graves disease
- being a receptive partner ("bottom") in anal sex
- having anal or genital warts
- having had an abnormal cervical screening test result
- having had cancer of the cervix, vulva or vagina
- smoking tobacco
- having unprotected sex
- having many sex partners
- being aged over 45.
Some people with anal cancer do not have any of these risk factors.
Learn more about cancer prevention
HPV vaccination
Vaccination can prevent infection with HPV. The most common HPV vaccine used in Australia protects against cancers linked with HPV including anal, cervical, vaginal and vulvar cancers.
Under the national HPV vaccination program, free vaccines are provided at school for all children aged 12–13.
Learn more
Symptoms
In its early stages, anal cancer often has no obvious symptoms, but symptoms can include:
- blood or mucus in faeces or on toilet paper
- itching, discomfort or pain around the anus, or a feeling of fullness, discomfort or pain in the rectum
- a lump near the edge, or inside, of the anus
- ulcers around the anus
- difficulty controlling bowel movements
- feeling that the bowel hasn't been emptied completely.
Not everyone with these symptoms has anal cancer. Other conditions, such as piles (haemorrhoids) or tears in the anal canal (anal fissures), can also cause these changes.
If symptoms are ongoing, see your general practitioner (GP) for a check-up.
“The diagnosis of anal cancer was a huge shock and overwhelming. Being poked and prodded there was initially intimidating. But my focus was on doing everything I could to get well.” Annie
Diagnosis and staging
The main tests for diagnosing anal cancer are a physical examination and endoscopy with biopsy.
- Physical examination – The doctor inserts a gloved finger into your anus to feel for any lumps or swelling. This is called a digital anorectal examination (DARE).
- Endoscopy – The doctor inserts a narrow instrument called a sigmoidoscope or colonoscope into your anus to see the lining of the anal canal. This may be done under a general anaesthetic (sedation).
- Biopsy – Only a tissue sample (biopsy) from the area can be used to diagnose cancer. This sample may be collected during the endoscopy, and then sent to a pathologist who will check it for cancer under a microscope.
- Imaging scans – These are used to check if cancer has spread. Scans may include a pelvic MRI, an ultrasound, a CT scan or, less often, a PET-CT scan.
Staging anal cancer
Staging describes how far the cancer has spread. Knowing the stage helps doctors plan the best treatment for you. Anal cancer is staged using the TNM (Tumour Nodes Metastasis) system:
- T (Tumour) 0–4 indicates how far the tumour has grown into the bowel wall and nearby areas. T1 is a smaller tumour (2cm or less) and T4 can be any size but growing into surrounding organs.
- N (Nodes) 0–1c shows if the cancer has spread to nearby lymph nodes (small glands). N0 means no cancer is in the lymph nodes, N1 means cancer is in the lymph nodes around the rectum, groin and/or pelvis. N1 can be further divided into a, b or c, depending on which lymph nodes the cancer has spread to.
- M (Metastasis) 0–1 shows if the cancer has spread to other, distant parts of the body. M0 means the cancer has not spread and M1 means the cancer has spread.
Understanding Anal Cancer
Download our Understanding Anal Cancer fact sheet to learn more.
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