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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.
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.
About 8 out of 10 anal cancers (80%) are squamous cell cancers. They are also called epidermoid cancers.There are 3 types:
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.
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.
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.
Risk factors include the following:
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:
The following tests and procedures may be used:
The prognosis (chance of recovery) depends on the following:
The treatment options depend on the following:
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
Page last updated: 04/05/2020