Risks and causes of anal cancer
Anything that can increase your risk of getting a disease is called a risk factor.
Different cancers have different risk factors. Experts decide on a risk factor after studying the population and specifically looking at groups of people who have this cancer. It’s not usually possible to say what has caused cancer in an individual.
Many people who have these risk factors never get it. And some people with none of the risk factors can still develop it.
Your risk of developing anal cancer depends on many things, including age and lifestyle factors. Having HPV is the biggest risk factor for anal cancer. Most of us have HPV at some point during our life. But for most people, it won't cause anal cancer.
Human papilloma virus (HPV)
People with HPV have an increased risk of developing anal cancer. Around 90 in 100 cases of anal cancer (around 90%) are linked to HPV infection.
HPV is a common infection that gets passed from one person to another through close skin-to-skin contact, usually during sexual activity. For most people the virus causes no harm and goes away on its own.
Types of HPV
There are many different types of HPV, most are harmless. But some can cause genital warts, and others can increase the risk of some types of cancer.
Of the different types of HPV, type 16 is the most common type of HPV linked to anal cancer.
Sex
Anyone who has been sexually active is at risk of HPV infection. And having HPV increases your risk of anal cancer. HPV is spread through any kind of sexual activity including:
- oral sex
- touching in the genital area
- vaginal sex
- anal sex
- sharing sex toys
You can reduce the risk of getting HPV by using barrier methods such as condoms and dental dams. This doesn’t provide complete protection, but it helps to reduce the risk.
Men who have sex with men have an increased risk of anal cancer compared to the general population. The HPV vaccine is now offered to teenage boys and some men, including men who have sex with men. This means this risk may change in the future due to the protection from the HPV vaccination.
The HPV Vaccine
There is a vaccine to prevent HPV infection. All children aged between 11 and 13 in the UK are routinely offered the HPV vaccine at school.
These vaccines protect against the types of HPV that are most likely to cause cancer such as cervical and anal cancer. They don’t protect against all types of HPV.
The HPV vaccination works better in people who have never had an HPV infection. So the vaccination programme is offered at a young age, when people are less likely to have been exposed to HPV through sexual experiences.
Men aged 45 or under who have sex with men, are able to have the HPV vaccine on the NHS at a sexual health clinic or HIV clinic.
Some transgender people can also have the HPV vaccine on the NHS at a sexual health clinic or HIV clinic:
- trans women (women who were assigned male at birth) who are age 45 and under - doctors decide this on a case by case basis.
- trans men (men who were assigned female at birth) who are age 45 or under and who have sex with other men
But if you have had the vaccine when you were at school, there is no need to have it again.
Age and gender
The anal canal is the part of the anus that connects the rectum to the area of skin around your anus (anal margin). The risk of developing cancer in the anal canal increases as you get older.
Around 25 out of 100 people (around 25%) diagnosed with anal canal cancer each year in the UK are aged 75 and over.
It is also more common in women than men. But as anal cancer is rare the risk is still small.
There are no figures available on how age or gender affect the risk of cancer in the anal margin. This is because anal margin cancer is often classed as a skin cancer for statistics.
Human Immunodeficiency Virus (HIV)
Having the 
increases your risk of developing anal cancer. Having treatment for HIV reduces the risk.
Smoking
Some studies have shown smoking may increase the risk of anal cancer. Quitting smoking can reduce your risk of developing many types of cancers and it is never too late to stop.
Although it can be difficult to stop smoking, there are a range of support services and different products to help you.
History of cervical, vaginal or vulval cancer
Some studies show that if you have had cervical, vulval or vaginal cancer you have a higher risk than the general population of developing abnormal cells in the anus or anal cancer. The risk is also higher for women with a history of abnormal cells in the cervix, vulva or vagina.
This is probably due to HPV infection which is a risk factor common to all these cancers.
Having a weakened immune system
Your fights infection and diseases. If you have a weakened immune system, you are at greater risk of developing anal cancer compared to the general population.
The immune system can be affected by autoimmune diseases. These cause the body to attack its own tissue. (SLE), and are all autoimmune diseases. Some studies show that having one of these diseases may increase the risk of anal cancer.
People who take medicines to dampen down their immune system after an are at an increased risk of anal cancer. This is because they are more at risk of HPV infection.
Speak to your doctor if you are worried about the risk.
Are there other causes?
Stories about possible cancer causes are often in the media and it can be hard to know what’s true and what’s not. You may have heard of something that isn’t included here. This is because we only include a risk factor in this information if it is supported by good quality evidence.
Reducing your risk
There are ways you can reduce your risk of cancer.
