The "anal pap" is a screening tool used in at-risk populations to identify individuals who have premalignant cytologic changes in their anal epithelium.
The incidence of anal cancer in the general population is less than one case per 100,000. However, when evaluating specific high-risk populations, such as women with cervical lesions and cervical and vulvar cancers, men who are HIV negative with high risk behaviors, and men or women who are HIV positive, the rate is as high as 70 cases per 100,000. Several biological similarities are shared between cervical and anal cancers, including an association with Human Papilloma Virus (HPV) infections.
Anal cytology is suggested as a screening test for selected patients at high-risk for anal squamous intraepithelial lesions (ASIL).
There are no official guidelines regarding anal cytology screening for ASIL. The following patient group information is based on the approach used by the Palefsky group at University of California at San Francisco which is spearheading the clinical research on anal dysplasia (Palefsky 2001).
HIV-negative men or women with a history of receptive anal intercourse or anal warts.
HIV-positive men with a history of anal intercourse or anal warts. Some clinicians screen patients with CD4 counts that are less than 500/mm3 more frequently.
HIV-negative women with a history of anal warts, high-grade cervical squamous intraepithelial lesions (SIL)/carcinoma, or vulvar SIL/carcinoma.
HIV-positive women. Some clinicians screen patients with CD4 counts that are less than 500/mm3 more frequently.
Consider screening patients with organ transplants on chronic immunosuppressive agents.
Anal squamous intraepithelial lesions (ASIL) may be detected in the anal canal and most likely represent the precursor to anal cancer.
ASILs range from low to high grade. High-grade squamous intraepithelial lesions (HSIL) most likely represent true invasive cancer precursor lesions in the cervix, and most likely in the anus. Atypical squamous cells of undetermined significance (ASCUS) may also be found on cytologic examination in both the cervix and the anus, and these lesions are often accompanied by biopsy-proven SIL.
Anoscopic and histologic assessment of anal lesions is critical to classify the lesions accurately, since the grade of anal cytology often does not correspond to that of histology, which remains the gold standard. Still, anal cytology appears to play an invaluable role in detecting and treating high-grade dysplastic lesions before they progress to anal cancer. Any cytologic abnormality should be followed up with high resolution anoscopy and any lesion should be biopsied to confirm the grade of dysplasia.
Anal cytology reports will generally follow the format for cervical cytology. The absence of columnar cells in the smear does not reflect the validity of the sample. The sensitivity, specificity, and predictive value do not hinge on the presence or absence of columnar cells. Some sources, however, recommend that both squamous and columnar cells should be present in samples for adequate interpretation of slides.
Specimen Required: The methodology for this assay is routine cytopathologic evaluation using either conventional smears or the ThinPrep® method.