Introduction to Anal Cancer

Executive Summary

Anal cancer is the cancer of the anus, which begins when healthy cells of the anus change, forming a tumor mass that can be either cancerous or benign. Different cell types of the anus can become cancerous. Depending on the cell type, anal may be classified into squamous cell carcinoma, croacogenic tumour, adenocarcinoma, basal cell carcinoma, and melanoma.

Anal cancer is an uncommon type of cancer that occurs in the anal canal. Anal cancer is a disease in which malignant (cancer) cells form in the tissues of the anus. Hence, most anal cancers are related to human papillomavirus (HPV) infection.

The anus is the end of the large intestine, below the rectum, through which stool (solid waste) leaves the body. After digestion, the food, it passes from the stomach to the small intestine. It then moves from the small intestine into the main part of the large intestine (called the colon). And then, the colon absorbs water and salt from the digested food. While, the waste matter that’s left after going through the colon is known as faeces or stools. The stool is stored in the last part of the large intestine, called the rectum. From there, the stool is passes out of the body through the anus as a bowel movement.

The inner lining of the anal canal is the mucosa. Most anal cancers start from cells in the mucosa. Glands and ducts (tubes leading from the glands) are usually under the mucosa. The glands make mucus, which acts as a lubricating fluid.

What is Anal cancer

Anal cancer is the tumour of the anus. It usually affects the anal canal, a short tube at the end of the rectum, through which the stool leaves the body.

Cancer begins when healthy cells in or around the anus change and become unmanageable, forming a tumor mass that can be either cancerous or benign. Malignant tumors are those which can grow and spread to other body parts. However, a benign tumor can grow but cannot spread. During the development of cancer there can be many observable cell changes.

Studies have reported that some of these abnormal changes are the first step in the series of slow changes that lead to anal cancer. Sometimes abnormal cells disappear without treatment. However, these abnormal cells can also become cancerous. Such type of abnormal cell proliferation is called Dysplasia. Anal dysplasia is known as intraepithelial neoplasia(AIN) or squamous intraepithelial neoplasia (SIL). Growth such as polyps and warts may also appear in or around the anus. These growths can become cancerous over time. In some cases, to prevent the spread of anal tumour, it may be necessary to remove the precancerous tissue​1​.

Most anal cancers are related to human papillomavirus (HPV) infection. Signs of anal cancer include bleeding from the anus or rectum or a lump near the anus.

Tests that examine the rectum and anus helps to diagnose anal cancer.

Risk factors for anal cancer include the following:

  • Human papillomavirus (HPV) infection.
  • Having a condition or disease that causes a weakened immune system, such as human immunodeficiency virus(HIV) or an organ transplant.
  • Personal history of vulvar, vaginal, or cervical cancers.
  • Many sexual partners.
  • Having receptive anal intercourse (anal sex).
  • Smoking cigarettes.

These and other signs and symptoms may be due to anal cancer or by other conditions. Check with your doctor if you have any of the following:

  • Bleeding from the anus or rectum.
  • A lump near the anus.
  • Pain or pressure in the area around the anus.
  • Itching or discharge from the anus.
  • A change in bowelhabits.

Also Read: Symptoms based on Cancer types

Staging of Anal Cancer

Stage 0

In stage 0, abnormal cells are in the mucosa (innermost layer) of the anus. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called high-grade squamous intraepithelial lesion (HSIL).

Stage I

In stage I, cancer has formed and the tumour is 2 centimetres or smaller.

Stage II

Stage II anal cancer is divided into stages IIA and IIB.

  • In stage IIA, the tumour is larger than 2 centimetres but not larger than 5 centimeters.
  • In stage IIB, the tumor is larger than 5 centimeters.

Stage III

Stage III anal cancer is divided into stages IIIA, IIIB, and IIIC.

  • In stage IIIA, the tumour is 5 centimetersor smaller and has spread to lymph nodes near the anus or groin.
  • In stage IIIB, the tumor is any size and has spread to nearby organs such as the vagina, urethra, or bladder. Cancer has not spread to lymph nodes.
  • In stage IIIC, the tumor is any size and may have spread to nearby organs. Cancer has spread to lymph nodes near the anus or groin.

Stage IV

In Stage IV, the tumour is any size. Cancer may have spread to lymph nodes or nearby organs and has spread to other parts of the body, such as the liver or lungs.

Types of anal cancers

Squamous cell carcinoma

This cancer in the anal canal have grown beyond the surface and into the deeper layers of the lining. Squamous cell cancers of the anal margin (perianal skin) can be treated as an anal cancer or like squamous cell cancer of the skin. It is important to see an expert if you are diagnosed with perianal cancer to determine the best course of treatment. It is the most common type of anal cancer.


These cancers start in cells that line the upper part of the anus near the rectum. They can also start in the glands under the anal mucosa that release secretions into the anal canal. Most anal adenocarcinomas have the same treatment of rectal carcinomas. Adenocarcinomas can also start in apocrine glands  (a type of sweat gland of the perianal skin).


These cancers start in cells in the skin or anal lining that make the brown pigment called melanin. Only a very small number of anal cancers are melanomas. Melanomas are far more common on the skin in other parts of the body. If melanomas are found at an early stage (before they have grown deeply into the skin or spread to lymph nodes) they can be removed with surgery, and the outlook for long-term survival is very good. But because anal melanomas are hard to see, the diagnosis is late. If possible, the entire tumour is can be removed with surgery. A cure is possible if the complete removal of tumour takes place. .  If the melanoma has spread too far, other treatments may be necessary.

Anal Cancer Types

Different cell types of anus can become cancerous. Depending of the type of cell, anal cancer may be classified into various types. 

Squamous cell carcinoma is the most common form of anal cancer. Cancers begins in the outer layer of the anal canal.

Croacogenic cancers accounts for about 25% of all anal cancers. Such carcinoma occurs in cells that resemble squamous cell carcinoma. 

Adenocarcinoma begins with the glands that form mucus beneath the mucous membrane of the anus. 

Basal cell carcinoma is the cancer of the skin cells in and around the anus. 

Melanoma begins with cancer of the cells that produce colour in the inner layers of the skin or anus​2​.


  1. 1.
    Uronis HE, Bendell JC. Anal Cancer: An Overview. The Oncologist. Published online May 1, 2007:524-534. doi:10.1634/theoncologist.12-5-524
  2. 2.
    Salati S, Al K. Anal cancer – a review. Int J Health Sci (Qassim). 2012;6(2):206-230. doi:10.12816/0006000