This review considered the role of the anal Pap test as a screening test for anal dysplasia in patients at high risk of anal SCC. The screening process is now thought to be improved with the addition of testing for the human papillomavirus (HPV) in high-risk populations. High-resolution anoscopy (a method to view the rectal area, using an anoscope, a lighted instrument inserted into the rectum) rather than routine anoscopy-guided biopsy, is also now considered to be the diagnostic standard.
Clinical Need: Target Population and Condition
Anal cancer, like cervical cancer, is a member of a broader group of anogenital cancers known to be associated with sexually transmitted viral HPV infection. Human papillomavirus is extremely prevalent, particularly in young, sexually active populations. Sexual practices involving receptive anal intercourse lead to significantly elevated risk for anal dysplasia and cancer, particularly in those with immune dysfunctions.
Anal cancer is rare. It occurs at a rate of about 1 to 2 per 100,000 in the general population. It is the least common of the lower gastrointestinal cancers, representing about 4% of them, in contrast to colorectal cancers, which remain the third most commonly diagnosed malignancy. Certain segments of the population, however, such as HIV-positive men and women, other chronic immune-suppressed patients (e.g., after a transplant), injection drug users, and women with genital dysplasia /cancer, have a high susceptibility to anal cancer.
Those with the highest identified risk for anal cancer are HIV-positive homosexual and bisexual men, at a rate of 70 per 100,000 men. The risk for anal cancer is reported to be increasing dramatically in HIV-positive males and females, particularly since the introduction of highly active antiretroviral therapy in the mid-1990s. The introduction of effective viral therapy has been said to have transformed the AIDS epidemic in developed countries into a chronic disease state of long-term immunosuppression. In Ontario, there are about 25,000 people living with HIV infection; more than 6,000 of these are women. About 28% of the newly diagnosed HIV infections are in women, a doubling since 1999. It has also been estimated that 1 of 3 people living with HIV do no know it.
Health Technology Description
Anal Pap test screening involves the blind insertion of a swab into the anal canal and fixing cells either on a slide or in fluid for cytological examination. Anal cytology classified by the standardized Bethesda System is the same classification used for cervical cytology. It has 4 categories: normal, atypical squamous cells of uncertain significance, or squamous intraepithelial lesions which are further classified into low- or high-grade lesions. Abnormal cytological findings are subjected to further evaluations by high-resolution anoscopy, a technique similar to cervical colposcopy, and biopsy. Several HPV deoxyribonucleic acid detection technologies such as the Hybrid 11 Capture and the polymerase chain reaction are available to detect and differentiate HPV viral strains.
Unlike cervical cancer, there are no universally accepted guidelines or standards of care for anal dysplasia. Moreover, there are no formal screening programs provincially, nationally, or internationally. The New York State Department of Health AIDS Institute has recently recommended (March 2007) annual anal pap testing in high-risk groups. In Ontario, reimbursement exists only for Pap tests for cervical cancer screening. That is, there is no reimbursement for anal Pap testing in men or women, and HPV screening tests for cervical or anal cancer are also not reimbursed.
The scientific evidence base was evaluated through a systematic literature review. Assessments of current practices were obtained through consultations with various agencies and individuals including the Ministry of Health and Long-Term Care AIDS Bureau; Public Health Infectious Diseases Branch, Ministry of Health and Long-Term Care; Cancer Care Ontario; HIV/AIDS researchers; pathology experts; and HIV/AIDS clinical program directors. An Ontario-based budget impact was also done.
No direct evidence was found for the existence of controlled studies evaluating the effectiveness of anal Pap test screening programs for impact on anal cancer morbidity or mortality. In addition, no studies were found on the use of HPV DNA testing in the screening or diagnostic setting for anal dysplasia. The reported prevalence of HPV infection in high-risk groups, particularly HIV-positive males, however, was sufficiently high to preclude any utility of HPV testing as an adjunct to anal Pap testing.
Nine reports involving studies in the United States, United Kingdom, and Canada were identified that evaluated the performance characteristics of anal Pap test screening for anal dysplasia. All involved hospital-based specialty HIV/AIDS care clinics with mainly HIV-positive males. All studies involved experienced pathologists, so the results generally represent best-case scenarios. Estimates of anal Pap test sensitivity and specificity were highly variable, and depended on the varying prevalence of cytology abnormality and differential thresholds for abnormality for both cytology and histopathology.
In the largest study of HIV-positive males, sensitivity varied from 46% (95% confidence interval [CI], 36%–56%) to 69% (95% CI, 60%–78%). Specificity ranged from 59% (95% CI, 53%–65%) to 81% (95% CI, 76%–85%). In the only study of HIV-negative males, sensitivity ranged from 26% (95% CI, 5%-47%) to 47% (95% CI, 26%–68%). Specificity ranged from 81% (95% CI, 76%–85%) to 92% (95% CI, 89%–95%).
In comparison, cervical Pap testing has also been evaluated mainly in settings where there is a high prevalence of the disease, and estimates of sensitivitykij and specificity were also low and highly variable. In a systematic review involving cervical Pap testing, sensitivity ranged from 30% to 87% (mean, 47%) and specificity from 86% to 100% (mean, 95%).
No direct evidence exists to support the effectiveness of an anal Pap test screening program to reduce anal cancer mortality or morbidity. There are, however, strong parallels with cervical pap testing for cervical cancer. Sexually transmitted HPV viral infection is currently the acknowledged common causative agent for both anal and cervical cancer. Anal cancer rates in high-risk populations are approaching those of cervical cancer before the implementation of Pap testing.
The anal Pap test, although it has been mainly evaluated only in HIV-positive males, has similar operating characteristics of sensitivity and specificity as the cervical Pap test. In general, the treatment options for precancer dysplasia in the cervix and the anus are similar, but treatment involving a definitive surgical resection in the anus is more limited because of the higher risk of complications. A range of ablative therapies has been applied for anal dysplasia, but evidence on treatment effectiveness, tolerability and durability, particularly in the HIV-positive patient, is limited.