Anal pre-cancer (anal intraepithelial neoplasia)

What are anal High grade Squamous Intraepithelial Lesions (HSIL)?

HSIL is the name given to the certain abnormal cells in the anal canal. HSIL, if untreated, may progress to anal cancer in a small proportion of people. HSIL is also known as Anal Intraepitheliall Neoplasia (AIN), grades 2 and 3.

Where does HSIL occur?

Anal HSIL may be described according to where it is found:

  1. Perianal – when it develops just outside the anus, within 5cm of the edge of the anus
  2. Intra-anal – when it occurs inside the anus, mostly within the first 5cm inside the anus

It is possible to have anal HSIL in both sites at the same time.

What does anal HSIL mean for HIV-negative gay men?

Around 20% of HIV-negative gay or bisexual men have anal HSIL. It has been estimated that around 1 in 4000 such men will progress to cancer each year.

What does anal HSIL mean for HIV-positive gay men?

Around 30% of HIV-positive gay or bisexual men have AIN. It has been estimated that around 1 in 400 such men will progress to cancer each year.

What does anal HSIL mean for women?

A small, unknown, proportion of women develops anal HSIL. It approximately 10 times more common in women who have a history of cervical abnormalities.

HIV-positive women are also at higher risk. It is important that all HIV-positive women have regularly cervical Pap smears.

What are the symptoms of anal HSIL?

Most people who have anal HSIL have no symptoms and don't know they have it. If symptoms do occur, they include discolouration of the skin, itch, pain, lumpy skin or bleeding.

What causes anal HSIL?

Anal HSIL occurs in a minority of individuals following infection with high risk HPV, especially type 16. Anal warts are more typically due to different types of HPV (“low risk”) types – these are most commonly types 6 and 11.

What is Human Papilloma Virus (HPV)?

HPV is the most common sexually transmitted infection (STI) in the world. Anogenital HPV infection is divided into two groups:

“High risk” types, of which HPV type 16 is the most common. Other high risk types include types 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 73, and 82.

“Low risk” types, of which HPV type 6 is the most common. These are most often associated with benign anogenital warts. Other low risk anogenital HPV types include HPV 11, 42, 43, and 44.

How common is HPV and what are the symptoms?

Because infection is so common, most people encounter HPV very early on in their sexual careers. The majority of people infected with HPV have no symptoms or signs and their immune systems successfully get rid of it. However, in a minority of people, the infection persists. A minority of those with persisting HPV can then go on to develop symptoms.

Warts typically appear as single or multiple soft, moist, or flesh-coloured bumps in the genital areas. They sometimes appear in clusters that resemble cauliflower-like bumps, and may be raised or flat, small or large.

How is HPV transmitted?

HPV is very infectious and is spread by skin-to-skin contact during oral, vaginal, or anal sex with an infected partner. It can also be spread by non-penetrative and oral sex.

How can transmission be prevented?

The only way to prevent getting an HPV infection is to avoid direct skin-to-skin contact with an infected person. Using condoms may partially reduce your risk of HPV. However, condoms, do provide excellent protection against other STIs, including HIV.

There are a number of vaccines that can protect people against acquiring HPV, but they must be given before initial exposure to the particular HPV type. For this reason, they are most effective when given before the onset of sexual activity. These vaccine include Gardasil, Cervarex and Gardasil 9.

How is HPV treated?

Currently there is no known cure for HPV infection.
Genital warts sometimes disappear without treatment, but there is no way to predict whether warts will grow or disappear. There are several creams and solutions available for their treatment, depending on their size and location. Some lesions may also be treated by freezing, burning or laser treatment. Although these treatments remove the warts, they do not remove the virus. Thus, as HPV may still be present after such treatment, warts often come back.

Can I get tested for HPV infection?

There are number of tests now available that will detect the presence of HPV infection. Testing for high risk HPV infection is increasingly done in clinical practice, as part of screening procedures, and to monitor response to treatment.

What tests can be done to diagnose anal HSIL?

"Mosaicism", "punctuation" and ulceration - signs of anal pre-cancer seen at HRA
  1. Inspection: Close examination of the external anal area by a specialist can sometimes suggest a diagnosis of AIN. However, changes can often be very subtle and easily missed. Internal anal AIN can rarely be diagnosed by looking at the area, even when using an instrument such as a proctoscope.
  2. Anal Papanicolaou (“Pap”) smears
  3. High Resolution Anoscopy (HRA)
  4. Biopsies: These may be taken from the outside of the anus (perianal biopsy) or internally.

How is anal HSIL treated?

If you have anal HSIL, it is important that you discuss the matter carefully with your doctor. The body has the capacity to clear small areas of anal HSIL, and so it may be appropriate to simply monitor the situation carefully.
The most commonly used treatments are: surgical removal, laser, diathermy and the application of agents such as imiquimod. Your specialist will be the best person to discuss which approach is the most appropriate for you. Although likely, there is currently no hard evidence that any of these treatments reduce the risk of development of anal cancer.

What should I do if I am worried about anal HSIL?

Talk things over with your doctor, who will perform an initial assessment. If necessary, then you can be referred to a specialised service. If you are uncomfortable about talking over such matters with your doctor, Sexual Health Clinics often offer very useful advice.

More information is available at a number of sites, including: