Anal Intraepithelial Neoplasia (AIN)

AIN is short for anal intraepithelial neoplasia and it is often referred to as ‘anal precancer’, as some forms of it can be serious, but, it is important to be clear that it is not cancer

  • Neoplasia: microscopic cell changes seen as cells undergo the process of becoming cancerous
  • Intraepithelial: the abnormal cells have not got further than the epithelium or the lining of the anus

If you have been told you have AIN it is likely that it has been found due to a biopsy that has been taken, on an anal smear test, or, on looking with a microscope at the peri-anus (the skin around the anus) and the anal canal.

What causes AIN?
In 90% of cases, AIN is linked to infection with the human papillomavirus (HPV). HPV infection is extremely common. Not everyone who comes into contact with the HPV virus will get AIN. HPV virus also causes warts. Not everyone who has had warts will develop AIN.

Why do some people infected with HPV get AIN and some do not?
Not everything is known yet about AIN.
We know that immunosuppression of any kind weakens the body’s defences against the HPV virus and makes AIN more likely, often some years later. This includes

  • HIV infection (even if well-controlled)
  • Organ transplants
  • Inherited immune defects
  • Immune-suppressing drugs 

AIN is more common in those who practise receptive anal sex, especially men who have sex with men (MSM), and are HIV positive. Smoking is a known risk factor for AIN and anal cancer. However, some people have AIN without any risk factors.

It is hoped that the HPV vaccine will eventually make AIN rare, however as far as we know at present, once you have been infected with HPV (which most sexually active people have been), the vaccine will not work to treat or prevent AIN.

How should AIN be treated?
A study (LOPAC) is underway to compare treatment with close surveillance of high grade AIN in those immunosuppressed patients at highest risk, to answer the question as to which is the best way to prevent high grade (HSIL) becoming cancer.

At present, we suggest

  1. If you have low-grade AIN then you do not need treatment. We will suggest that testing is repeated in the future.
  2. If you have high grade AIN or HSIL of the anus then we will suggest follow up with HRA (high resolution anoscopy).
  3. For persistent areas, and wide areas of AIN, topical treatment (creams you apply yourself) can be used: imiquimod (Aldara) and 5 fluorouracil are both types of cream that can be prescribed for use 2-3 times weekly for 3-4 months. This treatment is most successful for AIN in the skin around the anus.
  4. In some cases, laser ablation of the AIN/HSIL is suggested. We are waiting for the results of the LOPAC study to give us the scientific evidence that will show whether laser intervention is more likely to prevent anal cancer than just close observation.

Patient journey

Patients are referred to the HANS service by their GP or other specialist. At present, it is not possible for people to refer themselves to the service. 

Once a referral is made, then the patient is contacted with an appointment for an assessment. Every effort is made to see patients for assessment at the earliest possible time.

The patient is sent an appointment date and time. If it is not convenient then a new appointment can be made, but this may be some time later.

During the assessment appointment, the doctor will ask questions about the patient's medical history and will make an examination. If necessary the doctor will take biopsies for a specific diagnosis. 

Your next appointment
Following the assessment appointment and possible biopsies, there will be a gap of 4-8 weeks. During this time the clinicians review the assessment and biopsy results and decide on the next stage. There are 3 possible outcomes:

  1. The patient is discharged: The doctors have reviewed the examination results and decided that there is no need to return.
  2. The patient may be put on surveillance: The doctors have reviewed the examination results and decided that they would like to keep an eye on the patient who is sent an appointment, usually for 6 months later.
  3. The doctors have reviewed the examination results and decided that the patient should be offered treatment. Typically the clinician will phone the patient and describe the kind of treatment that is recommended and an appointment is made. There are different kinds of treatments and the clinician will explain the recommended treatment.

More detailed information about the HANS service, the methods of examination and forms of treatment, is available from the menu options on the left of this screen, and can be downloaded. 

High resolution anoscopy

High resolution anoscopy, or HRA, is a procedure that allows for examination of the anal canal and surrounding skin using a microscope similar to a colposcope (used in the examination of the neck of the womb). This procedure is use to check for abnormal cells that have a higher likelihood of turning into cancer.

HRA is an outpatient procedure. It is usually well tolerated with only mild, if any discomfort. The microscope/colposcope provides magnification of up to 40 times. With it, the clinician performing the exam can detect any abnormal cells.

Taking a biopsy
After careful and thorough examination, the clinician may decide to take a biopsy. This is a small sample of tissue (4mm size) that is sent to the laboratory for analysis. A local anaesthetic will be given before the biopsy to minimise any discomfort. Healing of the biopsy sites occurs over 4-7 days, usually without any scarring.

Image of an internal sphincter

Biopsy results
Once the clinicians receive the biopsy results, they will send you a letter and a copy to your GP.  If they have suggested treatment, then the HANS office will write to you with an appointment.

HPV, anal warts & anal dysplasia

HPV stands for the human papillomavirus. It is a very common virus that is spread by direct contact, and infects skin cells and  moist membranes that line different parts of the body, including the mouth, throat and genital area.

There are over one hundred types of HPV and about 40 of these can affect the genital area. Some types of HPV can cause skin warts and verrucas but many types do not cause any problems or harm at all

Most adults get HPV at some point in their lives, and in most cases your body will get rid of the virus without you ever knowing you had it. However HPV is also linked to the development of abnormal cells. If left untreated, these abnormal cells may go on to develop into cancer.

What are the symptoms of HPV, anal warts and anal dysplasia? 

  • Patients with “dormant” HPV infection or a small number of anal warts usually have no symptoms. Other patients may notice small growths in the anal area that may increase in size or number. They may experience anal itching, burning or tenderness, anal bleeding, or anal discharge. In some patients, the warts may become very large and cause pain, significant discharge and odour, or interfere with the ability pass bowel movements.
  • In men, genital warts mainly appear on the penis and scrotum.
  • In women, they tend to be seen on the vulva, vagina and cervix.
  • Both sexes may be affected in the perineum, around the anal area and inside the anal canal.

How is HPV treated?
There are three main treatments for HPV related disease: chemical destruction, immune therapy, and surgical treatment. The clinician will advise the best treatment based upon their examination and the biopsy results.

It is important to realise that regardless of the treatment, recurrence of HPV is common. Skin cells outside of the visible area of disease may already be infected and not detectable until new warts form. 

Is there an HPV vaccine?
At the time of writing, two vaccines are available for HPV, Cervirax and Gardasil. Those vaccines are developed specific for 2 or 4 subtypes of HPV including those most likely to cause cancer. HPV vaccination is part of the national vaccination programme and is currently given to girls around the age of 12 years.

Vaccination is currently not recommended for the prevention of anal cancer, precancerous or dysplastic lesions, and genital warts caused by HPV. Studies are under way to determine effectiveness in those circumstances. 

Homerton Anogenital Neoplasia Service.

The Homerton Anogenital Neoplasia Service is a referral centre that provides a screening and treatment service for people at risk, or, who have developed, precancerous lesions in the genital area. This includes the anal canal, the skin surrounding the anus, penis, vagina and vulva. We have a team of experts to give you information and look after you.

To contact HANS:
call 020 8510 5940

About anal cancer
Laser ablative treatment
Laser ablative treatment
HRA HPV AIN leaflet