This term means there are abnormal cells in the lining of the back passage (anus). It is also called anal squamous intraepithelial lesions (SILs). AIN is not cancer but the cells might develop into cancer in the future. This is diagnosed by taking a sample of skin (biopsy) to be examined under a microscope. It 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 abnormalAnother system for grading 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.Low grade SIL (AIN 1) doesn’t usually require treatment. Repeating the skin samples might be required to confirm a diagnosis. Treatment of High grade SIL (AIN 2 to 3) might include surgical excision for localised disease or skin creams such as imiquimod or 5 Fluorouracil (5-FU), if the disease is affecting multiple parts. Clinical review in clinic and arranging mapping biopsies under general anaesthesia every 6 months are key to ensure resolution and no progression to anal cancer.