Anal intraepithelial neoplasia (AIN)
Anal intraepithelial neoplasia (AIN) means there are abnormal 
in the lining of your anus. AIN is not cancer but the cells might develop into cancer in the future.
Whether you need treatment or not depends on how much the cells look like normal cells. This is called the grade of the cells.
What are the symptoms of AIN?
You may not get any symptoms. But if you do, they can include:
- your anus being itchy
- bleeding or passing
mucus from your anus - pain in your anus
These symptoms of AIN can be caused by other conditions such as piles (haemorrhoids). But they can also be caused by anal cancer, so it is important to see your doctor if you have any of these symptoms.
What causes AIN?
Research suggests that AIN is linked to the human papilloma virus (HPV).
This 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. There are many different types of HPV, most are harmless. But some can increase the risk of AIN if they remain in the body.
How do I know if I have AIN?
Your doctor checks for AIN by looking at your anus and taking a sample of tissue. They call this an anoscopy and biopsy.
A specialist doctor called a pathologist looks at the biopsy under a microscope. They can see if any of the cells are abnormal. And if they are, how abnormal they are. This is called the grade of the AIN.
AIN grades
AIN can be divided into 3 grades. These are numbered 1 to 3:
- AIN 1 – the cells are slightly abnormal
- AIN 2 - the cells are moderately abnormal
- AIN 3 - the cells are severely abnormal
Or doctors refer to AIN as a low grade or high grade squamous epithelial lesion (SIL). This is because most of the abnormal cells are a type of cell called .
- In low grade SIL (LSIL) the cells are slightly different to normal anal cells – this is the same as AIN 1
- In high grade SIL (HSIL) the cells are moderately to severely different from normal anal cells – this is the same as AIN 2 and AIN 3
Treatment for AIN
Low grade SIL (AIN 1)
Low grade SIL can go away on its own so you may not need treatment. Your doctor may arrange regular follow ups to check the SIL for any changes. Or they might suggest you get retested at a later date. This is to check if the cells have gone back to normal.
But for some people treatment can relieve symptoms such as burning, itching, and bleeding. Your doctor will talk to you about your treatment options.
High grade SIL (AIN 2 and AIN 3)
You will need treatment because the abnormal cells are less likely to get better on their own. They might develop into anal cancer, but the risk of this is very small. Your doctor will discuss the best treatment option for you. Treatments might include:
- skin creams such as imiquimod or 5FU
- destroy the cells using heat or laser (ablation)
- trichloroacetic acid – a liquid which your doctor or nurse puts directly on the SIL
Less often people may have surgery to remove the SIL.
These treatments are also used for different types of cancers. You can find out more about the treatments on our treatment pages. But remember AIN is not cancer.
If AIN develops into anal cancer
Unfortunately in a small number of people, high grade lesions can develop into anal cancer.
How big an anal cancer is and whether it has spread is called the stage of the cancer. Treatment depends on the stage but includes and surgery.
