Anal cancer

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Precancerous conditions of the anus

Anal intraepithelial neoplasia (AIN) is a precancerous condition that can develop in the anus. It is also called anal squamous intraepithelial lesions (SIL) or anal dysplasia.

AIN is when cells in or around the anus change and become abnormal. These cells are not yet cancer, but there is a higher chance they will become anal cancer if they aren’t treated.

Doctors describe AIN as either low grade or high grade, depending on how the cells look under the microscope. Low-grade AIN cells look much like normal cells and will often return to normal on their own. High-grade AIN cells look very abnormal under the microscope and usually don’t return to normal. High-grade AIN needs to be treated or it could develop into anal cancer.

Risk factors

Human papillomavirus (HPV) infection is the most important risk factor for developing AIN. Having more than one sex partner increases your risk of developing an HPV infection. The following risk factors increase the chance that an HPV infection will not go away on its own and may develop into AIN:


AIN does not usually cause any symptoms. Most people do not know they have AIN. If there are any symptoms, they may include:

  • itching
  • discharge
  • raised or scaly areas around the anus
  • warts


If you have symptoms or your doctor thinks you might have AIN, you will be sent for tests. Tests used to diagnose AIN may include:

  • anal swab to collect a sample of cells to be examined under a microscope (called anal cytology)
  • anoscopy (endoscopy of the anus)
  • biopsy


Treatment options for AIN include:

photodynamic therapy (PDT)

Treatment with drugs that become active when exposed to light (photosensitizers).

During PDT, the photosensitizer is applied to the skin or injected into a vein and cancer cells absorb it. After a period of time, the cancer cells are exposed to light, which activates the photosensitizer and destroys the cancer cells.

Also called photochemotherapy, photoradiation therapy and phototherapy.


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