Squamous Intraepithelial Lesion of the Anus in a Man With HIV Infection

Susan C. Ball, MD, MPH

Disclosures

AIDS Read. 2004;14(9) 

In This Article

Anal Cancer

Anal cancer is uncommon in the general population; cases occur twice as frequently in women as in men. The current rate of 0.9 cases per 100,000 persons represents a doubling of the frequency of this diagnosis since the mid-1990s. Certain portions of the population -- notably men who have sex with men (MSM) -- have rates of anal cancer that are far higher. It is estimated that the incidence of anal cancer among MSM is between 25 and 37 per 100,000, similar to the rate of cervical cancer among women in the days before PAP tests became routine.[1,2]

A recent report noted the rise of the age-adjusted incidence of anal cancer among white men in San Francisco County. The rate of approximately 4 per 100,000 during 1984 to 1990 rose to more than 20 per 100,000 during 1996 to 1999. Sexual orientation was not documented in this study, but 85% of men reported they had never been married.[3] Other factors that contribute to an increased risk of anal cancer include anal warts, smoking, anal fissures or fistula, hemorrhoids, and immunosuppression.[4]

Anal cancer makes up 1.5% of the neoplasms of the digestive system and includes several different types of cancer because of the varied histology of the anal canal. The anal verge, where the perianal skin meets the squamous epithelium of the anal canal, is the most distal point of the anus (Figure). The more distal anal margin includes sweat, sebaceous, and apocrine glands and extends approximately 5 to 6 cm from the anal verge. Above the anal verge is the anal canal, extending from the upper to the lower border of the internal anal sphincter. The anal canal consists of 3 zones: most of the canal is the squamous zone, which is above the verge and ends at the dentate, or pectinate, line, where there is squamous and transitional epithelium. This is known as the anal transitional zone (ATZ). Above the ATZ is the colorectal zone, which has columnar mucosa identical to that of the rectum.

Anatomy of the anus. (Reprinted with permission from Ryan DP, Compton CC, Mayer RJ. Carcinoma of the anal canal. N Engl J Med. 2000;342-792-800. Copyright © 2000, Massachusetts Medical Society. All rights reserved.)

Because of these different cell types, neoplasms of the anus can be squamous cell carcinomas, adenocarcinomas, and small-cell or poorly differentiated carcinomas.[5] Small-cell and poorly differentiated carcinomas of the anus are extremely rare. Adenocarcinomas of the anus are treated as rectal cancer. Seventy-five percent to 80% of cancers in the anus are squamous cell carcinomas.

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