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)
Men and women 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 by sexual contact. For most people the virus causes no harm and goes away without treatment.
Types of HPV
There are many different types of HPV, most are harmless, some cause genital warts, and others can cause cancer.
Of the different types of HPV, type 16 is the most common in 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.
Studies in the past have shown that men who have sex with men have an increased risk of anal cancer compared to the general population. But these studies were carried out before the introduction of the HPV vaccine in teenage boys and some men. So this risk factor may change with new research that can take into account the effects of HPV vaccination.
Vaccines
There are now vaccines to prevent HPV infection. All girls and boys aged 12 or 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 cancers such as cervical and anal cancer. They don’t protect against all types of HPV.
HPV vaccination works better in people who haven’t ever had an HPV infection. As HPV is mostly passed on through sexual contact, the vaccination programme is offered at a young age when people are less likely to have had sexual experiences.
Men who are 45 or under and have sex with men are able to have the HPV vaccine on the NHS when they go to a sexual health clinic or HIV clinic.
Some transgender people can also have the HPV vaccine:
- trans women (people who were assigned male at birth) can have the HPV vaccine if their risk of getting HPV is the same as men having sex with men who can have the HPV vaccine
- trans men (people who were assigned female at birth) can have the HPV vaccine if they have sex with other men and are aged 45 or under
Age and gender
Your risk of developing anal cancer increases as you get older.
Around 25 out of 100 people (around 25%) diagnosed with anal cancer each year in the UK are aged 75 and over. But as anal cancer is a rare cancer the risk is still small.
Anal cancer is more common in women than men.
Human Immunodeficiency Virus (HIV)
Having the human immunodeficiency virus (HIV) increases your risk of developing anal cancer.
Smoking
Some studies have shown smoking increases the risk of anal cancer. Giving up smoking can reduce your risk of developing many cancers.
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 of developing abnormal cells in the anus or anal cancer than the general population. The risk is also higher for women with a history of abnormal cells in the cervix, vulva or vagina.
This is probably due to risk factors common to all these cancers, such as HPV infection.
Having a weakened immune system
Your immune system 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.
People taking medicines to damp down their immune system after an organ transplant (for example, a kidney transplant) also have an increased risk of anal cancer.
Other possible causes
Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.
