On this page: About the anus | What is anal cancer? | How common is anal cancer? | What are the risk factors? | What are the symptoms? | Vaccination and screening | Diagnosis | Staging
About the anus
The anus is the opening at the end of the 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 motion, the muscles of the anus (sphincters) relax to release the solid waste matter known as faeces or stools.
What is anal cancer?
Anal cancer is cancer affecting the tissues of the anus. Cancer is a disease of the cells, the body’s basic building blocks. Our 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.
When cells don’t grow, divide and die in the usual way, they sometimes form a lump called a tumour. If the cells are cancerous, they can spread through the bloodstream or lymph fluid and form another tumour at a new site. This new tumour is known as secondary cancer or metastasis.
Types of anal cancer
Squamous cell carcinomas (SCCs)
Most anal cancers are squamous cell carcinomas (SCCs), which come from the flat (squamous) cells that line much of the anus. The term ‘anal cancer’ commonly refers to these SCCs, and this page focuses on this type of anal cancer.
A small number of anal cancers are adenocarcinomas, which start from cells in the anal glands. This type of anal cancer is similar to bowel cancer and is treated in a similar way. See our bowel cancer section for more information.
A very small number of anal cancers affect the skin just outside the anus. Known as perianal skin cancers, they are treated in a similar way to skin cancers that are found on other parts of the body. See our skin cancer section for more information.
How common is anal cancer?
Every year, about 400 people are diagnosed with anal cancer in Australia. It is more common over the age of 50 and is somewhat more common in women than in men. However, men who have sex with men have the highest incidence of any group. The number of people diagnosed with anal cancer is increasing, with three times more cases in 2011 than in 1984.
What are the risk factors for anal cancer?
About 80% of anal cancer cases are caused by a very common infection called human papillomavirus (HPV). HPV can affect the surface of different areas of the body, including the anus, cervix, vagina and penis. Unless they are tested, most people will not be aware that they have HPV as it usually doesn’t cause any symptoms.
HPV is the main risk factor for anal cancer, but other factors that may increase the risk of getting anal cancer include:
- having a weakened immune system, e.g. because of human immunodeficiency virus (HIV), an organ transplant or an autoimmune disease such as lupus
- having anal warts
- being a man who has had sex with other men
- being a woman who has had an abnormal cervical screening test result or cancer of the cervix, vulva or vagina
- having multiple sexual partners and unprotected anal sex
- being over 50
However, some people with anal cancer do not have any of these risk factors.
What are the symptoms of anal cancer?
In its early stages, anal cancer often has no obvious symptoms. However, some people may experience symptoms such as:
- blood or mucus in stools (faeces) or on toilet paper
- itching, discomfort or pain around the anus
- a feeling of fullness, discomfort or pain in the rectum
- a lump near the edge of the anus
- ulcers around the anus
- difficulty controlling bowels.
Not everyone with these symptoms has anal cancer. Other conditions, such as haemorrhoids or tears in the anal canal (anal fissures), can also cause these changes. However, if the symptoms are ongoing, see your general practitioner (GP) for a check-up.
Vaccination and screening
The human papillomavirus (HPV) is the main cause of anal cancer. Gardasil, a vaccine that protects against the most common types of HPV that cause cancer, is currently provided free of charge to Australian girls and boys in their first year of high school. The vaccine should also help lower rates of HPV-related cancers, but it will be some decades before that happens. The vaccine does not protect against all types of HPV, so it will not prevent all HPV-related cancers.
The HPV vaccine works best if given before exposure to HPV, that is, before a person becomes sexually active. However, it may still provide some benefit once a person is sexually active. Talk to your doctor about whether you or your partner/s should consider having the HPV vaccine.
Testing for cancer when there are no symptoms is known as screening. At present, screening for anal cancer is not recommended by any clinical bodies in any country. However, researchers are currently investigating the usefulness of screening tests, particularly for high-risk groups. The screening tests that are being studied include:
- digital anorectal examination (DARE) – the doctor inserts a gloved finger into your anus to feel for any lumps or swelling
- anal Pap test (also called anal Pap smear) – a small brush or spatula is inserted into the anus to collect some cells; the cells are examined under a microscope in a laboratory to check for abnormalities
- high-resolution anoscopy – a short instrument is inserted into the anus to create detailed images of the anal canal.
The main tests for diagnosing anal cancer are:
Your doctor inserts a gloved finger into your anus to feel for any lumps or swelling. This is called a digital anorectal examination (DARE).
Proctoscopy with biopsy
The doctor inserts a small, rigid instrument called a proctoscope into your anus to see the lining of the anal canal. This may be done under a local or general anaesthetic so that a tissue sample (biopsy) can be taken at the same time. The biopsy will be sent to a laboratory for testing.
If anal cancer is found, you may need one or more imaging scans to check whether it has spread. These scans may include an MRI, an endorectal ultrasound, a CT scan or an FDG-PET/CT scan. To find out about these tests visit your local Cancer Council website or call Cancer Council 13 11 20.
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; T4 is a larger tumour.
N (Nodes) 0–3
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; N2 means cancer is in pelvic and/or groin lymph nodes on one side; N3 means cancer is in pelvic and groin lymph nodes on one side, or on both sides.
M (Metastasis) 0–1
Shows if the cancer has spread to other, distant parts of the body. M0 means cancer has not spread; M1 means cancer has spread.
Reviewed by: Dr Tiffany Daly, Radiation Oncologist, Radiation Oncology Princess Alexandra Raymond Terrace (ROPART), QLD; Polly Baldwin, 13 11 20 Consultant, Cancer Council SA; Heather Kavanagh, Colorectal Cancer Nurse Coordinator, Royal North Shore Hospital, NSW; Judy Koch, Consumer; A/Prof Craig Lynch, Colorectal Surgeon and Chair, Colorectal Cancer Service, Peter MacCallum Cancer Centre, VIC; Dr David Millar, Sexual Health Physician, Perth Men's Health, WA; Julie O’Rourke, Clinical Nurse Consultant, Radiation Oncology, Canberra Hospital, ACT.