Anal pre-cancer (anal intraepithelial neoplasia)

What is anal intraepithelial neoplasia (AIN)?

AIN is the name given to the appearance of abnormal cells of the anal canal. High-grade AIN, if untreated, may progress to anal cancer.

Where does AIN occur?

AIN 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 AIN in both sites at the same time.

What does AIN mean for HIV-negative gay men?

In the United States, around 7% of HIV-negative gay or bisexual men have AIN. A small minority of such men will, over time, develop anal cancer, a disease estimated to affect 35 per 100,000 "unmarried single men" per year.

What does AIN mean for HIV-positive gay men?

In the United States, around 36% of HIV-positive gay or bisexual men have AIN. Although it is not yet conclusively known whether HIV status affects progression to anal cancer, anal cancer is thought to be more common in HIV-positive than HIV-negative men. In addition, clinical trials indicate that anal cancer in HIV-positive men may respond less well to treatment and may be associated with greater treatment-related side effects than anal cancer in HIV-negative men.

What does AIN mean for women?

A small, unknown, proportion of women develops AIN. It is thought to be more common in women who have a history of cervical abnormalities.

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

What are the symptoms of AIN?

Most people who have AIN 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 AIN?

The precise cause of AIN is not yet known and more research is required to identify the factors that put some people at greater risk than others. However, AIN is typically associated with anal infection by certain types of human papilloma virus (HPV), the health consequences of which can include the development of anal warts.

What is human papilloma virus?

Human papilloma virus (HPV) is the most common sexually transmitted infection (STI) in the world. There are high-risk and low-risk types of HPV. High-risk HPV types may be associated with abnormal anal Pap smear results, and are also associated with cancer of the anus.

Low-risk HPV types may be associated with abnormal anal Pap smear results and genital warts. People are typically infected with several different types of HPV at the same time.

How common is human papilloma virus and what are the symptoms?

Because infection is so common, most people who are sexually active will encounter HPV at some stage in their lives, often 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, and they may then go on to develop warts.

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 human papilloma virus transmitted?

Genital wart virus is very infectious and is spread by skin-to-skin contact during oral, vaginal, or anal sex with an infected partner. About two-thirds of people who have sexual contact with a partner with genital warts will develop warts, usually within 3 months of contact.

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 developing diseases linked to HPV, such as genital warts. Condoms, do, however, provide excellent protection against other STIs, including HIV.

It is possible that the vaccines designed to prevent cervical cancer may also, at least partially, help prevent the development of AIN & anal cancer. However, these vaccines must be given before the onset of sexual activity & they are still being evaluated in this role.

How is human papilloma virus 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. However, such testing is rarely done in clinical practice, as the results do not alter the management of the situation. Their use is largely restricted to research studies.

What tests can be done to diagnose AIN?

"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 AIN treated?

If you have AIN, it is important that you discuss the matter carefully with your doctor. The body has the capacity to completely heal itself from AIN, particularly AIN1 and so it maybe appropriate to simply monitor the situation.. 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 AIN?

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.