What are the risk factors?

About 80% of anal cancers are caused by infection with 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. Unless they are tested, most people won’t know they have HPV infection as it usually doesn’t cause symptoms.

HPV infection is the main risk factor for anal cancer, but other factors that may increase the risk include:

• having a weakened immune system, e.g. because of human immunodeficiency virus (HIV) infection, an organ transplant, or an autoimmune disease such as coeliac disease, lupus or Graves’ disease
• being a man who has had sex with other men
• having anal warts
• having had an abnormal cervical screening test or cancer of the cervix, vulva or vagina
• smoking tobacco
• being aged over 50.

Some people with anal cancer do not have any of these risk factors.