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Classification and epidemiology of anal cancer

David P Ryan, MD
Christopher G Willett, MD
Section Editor
Richard M Goldberg, MD
Deputy Editor
Diane MF Savarese, MD


Anal cancer is uncommon. It comprises only 2.5 percent of all digestive system malignancies in the United States; only 8080 new cases are diagnosed annually [1].

The incidence of anal cancer in the general population has increased over the last 30 years, both in the United States and elsewhere [2-6]. An increased incidence has been associated with female gender, infection with human papillomavirus (HPV), lifetime number of sexual partners, genital warts, cigarette smoking, receptive anal intercourse, and infection with human immunodeficiency virus (HIV) [7]. Thus, from an etiologic standpoint, anal cancer is more similar to genital malignancies than it is to gastrointestinal tract cancers.

Substantial progress has been made in the pathophysiology and treatment of anal cancer [8]. In the 1960s, this malignancy was thought to be due to chronic perianal inflammation and was treated routinely by abdominoperineal resection, necessitating a permanent colostomy [9]. As a result of carefully conducted epidemiologic and clinical studies, it is now known that anal cancer is associated with HPV infection and that cure of anal cancer is possible in the majority of patients with preservation of the anal sphincter.

The pathology and epidemiology of anal cancer will be reviewed here. The clinical features, diagnosis, and treatment are discussed separately. (See "Clinical features, staging, and treatment of anal cancer".)


The anal canal is 2.5 to 3.5 cm long and begins superiorly at the anorectal junction where the rectal ampulla is narrowed by the puborectalis sling. It ends at the anus. Externally, the anal canal is surrounded by the internal and external anal sphincter muscles (figure 1) [10]. The anal canal is divided by the dentate (pectinate) line, a macroscopically visible landmark that overlies the transition from glandular to squamous mucosa; immediately proximal to the dentate line, a narrow zone of transitional mucosa that is similar to urothelium is variably present.


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Literature review current through: Sep 2016. | This topic last updated: Feb 4, 2016.
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