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Anal cancer is a disease in which malignant (cancer) cells form in the tissues of the anus.

The anus is the end of the large intestine, below the rectum, through which stool (solid waste) leaves the body. The anus is formed partly from the outer, skin layers of the body and partly from the intestine. Two ring-like muscles, called sphincter muscles, open and close the anal opening to let stool pass out of the body. The anal canal, the part of the anus between the rectum and the anal opening, is about 1½ inches long.

Gastrointestinal (digestive) system anatomy; shows esophagus, liver, stomach, colon, small intestine, rectum, and anus.

Anatomy of the lower digestive system, showing the colon and other organs.

 The skin around the outside of the anus is called the perianal area. tumours in this area are skin tumours, not anal cancer.

Squamous cell carcinoma with variants of anal canal 

About 8 out of 10 anal cancers (80%) are squamous cell cancers. They are also called epidermoid cancers.

There are 3 types:

  • Large cell keratinising.
  • Large cell non keratinising (also called transitional).
  • Basaloid.

A keratinising cancer has keratin (the protein in your hair and nails) in the cancer cells. This type of anal cancer starts in the lower part of the anus. Non keratinising types start from the transitional zone of the anal canal. This is where the squamous cells meet the glandular cells. Many anal cancers have a mix of these cell types. 

Doctors treat all these squamous cell types of anal cancer in the same way.

Squamous cell carcinomas of the anal margin (perianal skin) are treated similarly to squamous cell carcinomas of the skin elsewhere in the body.

For more on Squamous cell carcinoma, click here.

Adenocarcinoma with variants of anal canal

This is a rare type of anal cancer that affects the glandular cells that produce mucus in the anal canal. Doctors treat this type of anal cancer in the same way as rectal cancer. More information on rectal cancer can be found here.

Adenocarcinoma of the anal canal accounts for 3 to 9% of all anal canal neoplasms. Differentiating true anal canal adenocarcinoma from low rectal adenocarcinoma can be challenging. Most anal canal adenocarcinomas originate from anal glands.

Multiple factors, including infection with HPV and HIV, history of receptive anal intercourse, smoking, and immunosuppression have been identified as risk factors. 

Clinical features include anal pain, induration of the anal canal, or abscess formation and a palpable lump. Evidence for treatment recommendations is based on small series and extrapolation from experience treating low rectal adenocarcinoma. Wide local excision can be performed for small well-differentiated tumours.

Reported disease-free 5-year survival varies from 21 to 58% according to the treatment modality. Local recurrence rates range from 20 to 37% at 4 years. 

Paget's disease of anal canal

Perianal Paget's disease is an uncommon disease, first described by Darier and Couillard in 1893, which is characterized by the presence of atypical Paget's cells in the anal and perianal epidermis. In 33% of the patients with perianal Paget's disease, the patients have an associated anorectal carcinoma.

Men and women are equally affected, with most cases occurring between the age of 40 and 60. The condition is generally indolent, but often recurs. Treatment options are generally wide local surgical excision or radiotherapy.

Being infected with the human papillomavirus (HPV) can affect the risk of developing anal cancer.

Risk factors include the following:

  • Being older than 50 years.
  • Being infected with human papillomavirus (HPV).
  • Having many sexual partners.
  • Having receptive anal intercourse (anal sex).
  • Frequent anal redness, swelling, and soreness.
  • Having anal fistulas (abnormal openings).
  • Smoking cigarettes.

Possible signs of anal cancer include bleeding from the anus or rectum or a lump near the anus.

These and other symptoms may be caused by anal cancer. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:

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

Tests that examine the rectum and anus are used to detect (find) and diagnose anal cancer.

The following tests and procedures may be used:

  • Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
  • Digital rectal examination (DRE): An exam of the anus and rectum. The doctor or nurse inserts a lubricated, gloved finger into the lower part of the rectum to feel for lumps or anything else that seems unusual.
  • Anoscopy: An exam of the anus and lower rectum using a short, lighted tube called an anoscope.
  • Proctoscopy: An exam of the rectum using a short, lighted tube called a proctoscope.
  • Endo-anal or endorectal ultrasound: A procedure in which an ultrasound transducer (probe) is inserted into the anus or rectum and used to bounce high-energy sound waves (ultrasound) off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.
  • Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. If an abnormal area is seen during the anoscopy, a biopsy may be done at that time.

Certain factors affect the prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) depends on the following:

  •   The size of the tumour.
  •   Where the tumour is in the anus.
  • Whether the cancer has spread to the lymph nodes.

The treatment options depend on the following:

  • The stage of the cancer.
  •   Where the tumour is in the anus.
  • Whether the patient has human immunodeficiency virus (HIV).
  • Whether cancer remains after initial treatment or has recurred.

For more information on Anal Cancer click here

This link is to the National Cancer Institute (NCI) cancer website in the United States. There may be references to drugs and clinical trials that are not available here in Australia.

Information has also been sourced from cancerresearchuk.org, ncbi.nlm.nih.gov, pathologyoutlines.com, jjco.oxfordjournals.org and cancer.org