Anal intraepithelial neoplasia (AIN) means there are abnormal cells in the lining of your anus. It is also called anal squamous intraepithelial lesions (SILs). This is because most of the abnormal cells are a type of cell called squamous cells.
A pathologist looks at your cells under a microscope to check whether your anal cells look different to normal anal cells.
AIN is not cancer but the cells might develop into cancer in the future.
Grading of anal intraepithelial neoplasia (AIN)
AIN is divided into grades 1 to 3. The grade relates to how abnormal these cells look under a microscope.
- AIN 1 – the cells are slightly abnormal.
- AIN 2 - the cells are moderately abnormal.
- AIN 3 - the cells are severely abnormal.
Another system doctors use refers to AIN or SIL as low grade or high grade:
- In low grade SIL (LSIL or AIN 1) the cells are slightly different to normal anal cells.
- In high grade SIL (HSIL or AIN 2 to 3) the cells are moderately to severely different from normal anal cells.
Treatment for AIN
Low grade SIL (AIN 1)
You might not need treatment. For some people treatment can relieve symptoms such as burning, itching, and bleeding. Your doctor will check your SIL by taking a sample of skin (biopsy). And they will arrange regular checks to monitor your SIL.
High grade SIL (AIN 2 to 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 them changing to a cancer is very small. Your doctor will discuss the best treatment option for you. Treatments might include:
- laser to destroy the cells (laser ablation)
- skin creams such as imiquimod or 5FU