Anal cancer is when malignant cancer cells form in the tissue in the anus. Anal cancer usually occurs in two areas: where the anal canal meets the rectum or in the skin just outside the anal opening.
The anus is a 4-cm section located at the end of the large bowel (or colon) that opens to the outside of the body. The anal canal connects the anus to the rectum (final section of the large intestine). The anus has an important role in controlling bowel motions. The sphincter muscles of the anus contract and relax to release solid waste called faeces or stools.
The most common form of anal cancer occurs in a type of cell that lines the surface of the anal canal called squamous cells. This type of cancer is a “squamous cell carcinoma” and represents around 75% of cases. 15% of anal cancer cases are “adenocarcinomas”, which form from cells in the anal glands. These glandular cells make the mucus that helps stools (faeces) pass more smoothly. Another rare type of anal cancer is melanoma, which begins in cells in the skin called “melanocytes”.
Early stages of anal cancer often do not cause any symptoms or only cause non-specific symptoms, which can be commonly found in other illnesses.
Anal cancer symptoms may include:
- Blood in stool or on the toilet paper
- Bleeding from the rectum. Nearly 50% of individuals diagnosed with anal cancer have had symptoms of rectal bleeding or blood in their stool.
- Bowel changes such as difficulty controlling bowel movements
- Discharge of mucus from the anus
- Pain, itching or discomfort in the area around the anus
- Feeling full, discomfort or pain in the rectum
- Feeling a lump near the edge of the anus
- Ulcers around the anus
If you experience any of these symptoms or have concerns, please contact your general practitioner (GP).
Anal cancer is a rare cancer, with approximately 591 people diagnosed in Australia each year. The risk of anal cancer increases with age but it can occur at any age. It is more common in women than men.
Cases of anal cancer have been increasing. Since 1982, cases of anal cancer increased from 0.65 per 100,000 to an estimated 1.9 in 2021.
Most common types of anal cancer have a very good long-term prognosis, especially if the cancer is found early. The five-year survival rate for anal cancer is 69.3%.
Over 80% of anal cancer cases are linked to infection of Human Papilloma Virus (HPV). HPV is a very common infection usually transmitted from different forms of sexual contact. Depending on the type of HPV, the virus can affect different parts of the human body, which include the anus, cervix, vagina, penis, throat and inside of the mouth. Anal cancer is caused by HPV16 and HPV18.
HPV can cause genital warts, common warts and some cancers, which include cervical, anal and throat and mouth cancer. However, for most healthy individuals, infection with HPV does not cause any symptoms.
There are also lifestyle and health factors that can increase your risk of developing anal cancer.
Risk factors for anal cancer include:
- Having a weakened immune system. Your immune system protects you from possible infections and diseases. A weakened immune system makes the individual at greater risk of developing illness. This can be caused by having Human Immunodeficiency Virus (HIV), organ transplantation or autoimmune diseases.
- Older age
- Having anal or genital warts
- Having unprotected sex
- Having multiple sex partners
- Men who have had sex with other men
- Women who have a medical history of cervical, vaginal or vulval cancer.
The type of diagnosis or tests will vary depending on the symptoms.
The medical practitioner will first conduct a physical examination called a DRE (or Digital AnoRectal Examination when the doctor will check for any abnormalities in the anus and rectum by inspecting and inserting a gloved lubricated finger into your anus.
A more detailed examination of the anus and rectum may also be done using a procedure called a proctoscopy. This is done by inserting a proctoscope, which is a long tube with a light, into the anus. This will allow the doctor to see the lining of the anal canal more clearly. During the procedure, the doctor may also take a small sample of tissue, called a biopsy, to examine under a microscope to see if there are any cancer cells.
There may also be blood tests to check for anaemia (low haemoglobin count due to bleeding from the rectum). Scans of the anus and nearby organs may be performed to create a clearer picture for doctors to see if there is any evidence of anal cancer or if it has spread. This can include Magnetic Resonance Imaging (MRI scans), computed tomography (CT scans) or an endorectal ultrasound.
The most common type of treatment for anal cancer is a combination of chemotherapy and radiotherapy, called chemoradiotherapy.
Chemoradiotherapy is a combination of radiotherapy courses with chemotherapy sessions. During chemotherapy, the individual will be given anti-cancer drugs that are toxic and will kill cancer cells. The chemotherapy also enhances the anti-cancer effects of radiotherapy on cancer cells. Drug doses are injected into a vein through an intravenous (IV) drip. Radiotherapy uses radiation to kill cancer cells so that they are unable to spread to the rest of the body. A machine directs the radiation specifically to target the location of the cancer while aiming to cause as little damage as possible to healthy cells.
Surgery may be recommended if the anal cancer is found early or if there are still cancerous cells remaining after chemoradiotherapy. However, it depends on the size and location of the tumour. It is possible to remove small anal cancer tumours that are located near the entrance of the anus using a type of surgery called local excision.
However, if chemoradiotherapy is not effective, a large operation called an abdominoperineal resection may be required. During an abdominoperineal resection, the surgeon removes the anus, rectum and part of the colon (large bowel). The surgeon will then use the remaining colon to create a stoma (also known as a colostomy). The stoma is permanent, and is an opening in the abdomen to allow faeces to leave the body. A colostomy bag will need to be worn to collect the faeces.
There is currently no routine anal cancer screening program in Australia.
The risk of developing anal cancer can be reduced by avoiding risk factors. This includes:
- Using condoms during sex. However, HPV can infect areas not covered by a condom so it is not completely protective against the virus.
- Vaccinations can protect against HPV infection. As more than 80% of anal cancer cases have been linked to HPV, preventing HPV infection can decrease the chances of developing anal cancer. A vaccine called Gardasil aims to protect against both virus types most likely to cause anal cancer: Type 16 and Type 18 of HPV. The vaccine also protects against Type 6 and Type 11 of HPV, which are responsible for 90% of genital warts. The vaccine can be effective even if an individual has already been exposed to one strain of HPV. The vaccine can still give the person protection from other HPV strains they are not infected with.
In Australia, the Gardasil vaccine is now part of a National Vaccination program provided free at schools for boy and girls aged 12-13 years old. The program is showing signs of dramatically reducing HPV virus incidence in Australia.
(For more information about Gardasil see: http://www.hpvvaccine.org.au/)
(For more information about the National HPV Vaccination program http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/immunise-hpv)
The vaccine is also available for people aged 14 years and older but it is not free. Please check with your doctor or local immunisation provider for more information.