Anal Pap smears are important to consider in men who have sex with men, especially those who are human immunodeficiency virus (HIV)-positive. Anal Pap smears also should be considered in men and women with a history of anogenital human papillomavirus (HPV) infection, anal receptive intercourse, multiple sexual partners, and a history of sexually transmitted disease or anal condyloma.1
The incidence of squamous cell carcinoma (SCC) of the anus in men who have sex with men is estimated to be 35 per 100,000.1 It is approximately the same incidence as that of SCC of the uterine cervix before the institution of screening programs using Pap smears. Carcinoma of the anus now represents about 1.5 percent of all cancers of the digestive tract. The American Cancer Society estimated that 4,010 new cases would be diagnosed in the United States in 2004, an increase from 3,400 cases in 2000. Approximately 620 patients will die of the disease this year.2
Anal cytology, when atypical squamous cells of undetermined significance (ASCUS) is included as an abnormal cytologic result, has 69 percent sensitivity in HIV-positive men and 47 percent in HIV-negative men. However, cost-effectiveness modeling has resulted in anal Pap smears being cost-effective if performed in HIV-positive men every year and in HIV-negative men every three years.3
How does one collect an anal Pap smear?
The sampling for anal Pap smears is easy to accomplish. A Dacron cotton swab should be used. Avoid using a cotton swab on a wooden stick, because these often break and will splinter. The patient may be placed in the lateral recumbent position. In women, the dorsal lithotomy position may be used as when completing a cervical Pap smear. The Dacron swab is inserted 5 to 6 cm without direct visualization. Firm lateral pressure is applied to the swab handle. It is rotated and slowly withdrawn from the anal canal.1 Make sure to sample the transition zone during removal, as this area, which separates the columnar epithelium of the rectum from the keratinizing anal squamous mucosa, is the site where most anal intraepithelial neoplasms arise.2
Do we use the ThinPrep container or do we prepare an old-fashioned
Liquid cytology is the preferred method for preservation. This eliminates artifact with drying and reduces the amount of fecal material and bacteria that can obscure cellular detail. However, air-drying and fixation may be used if liquid cytology is not available.
Criteria used to interpret HPV-related lesions of the anus and cervix are essentially the same. Coexisting infections also may be noted.1 These include herpes virus and cytomegalovirus infections and Candida. Other organisms such as amebic cysts, trophozoites, pinworm eggs, and strongyloides have been seen. Any report of ASCUS or higher on anorectal cytology requires an anal colposcopy. These are easily accomplished using an anoscope and a colposcope.
The question of testing for HPV has not been answered thoroughly.1 Rates of HPV positivity are high in the populations targeted for screening using anorectal cytology. The technology used for cervical samples has not been approved by the U.S. Food and Drug Administration for use in anorectal cytology. However, HPV testing does have a good negative predictive value.1
1. Darragh TM, Winkler B. The ABCs of anal-rectal cytology. CAP Today. College of American Pathologists, May 2004. Accessed online March 4, 2005, at:http://www.cap.org/apps/docs/cap_today/pap_ngc/NGC_analrec-talcyto.html.
2. Jemal A, Murray T, Ward E, Samuels A, Tiwari RC, Ghafoor A, et al. Cancer statistics 2005. CA Cancer J Clin. 2005;55:10–30.
3. Palefsky JM, Holly EA, Ralston ML, Jay N. Prevalence and risk factors for human papillomavirus infection of the anal canal in human immunodeficiency virus (HIV)-positive and HIV-negative homosexual men. J Infect Dis. 1998;177:361–7.