Anal intraepithelial neoplasia: A review of diagnosis and management

Abstract

Anal intraepithelial neoplasia (AIN) is a premalignant lesion of the anal mucosa that is a precursor to anal cancer. Although anal cancer is relatively uncommon, rates of this malignancy are steadily rising in the United States, and among certain high risk populations the incidence of anal cancer may exceed that of colon cancer. Risk factors for AIN and anal cancer consist of clinical factors and behaviors that are associated with the acquisition and persistence of human papilloma virus (HPV) infection. The strongest HPV-associated risk factors are HIV infection, receptive anal intercourse, and high risk sexual behavior. A history of HPV-mediated genital cancer, which suggests infection with an oncogenic HPV strain, is another risk factor for AIN/anal cancer. Because progression of AIN to anal cancer is known to occur in some individuals over several years, screening for AIN and early anal cancer, as well as treatment of advanced AIN lesions, is reasonable in certain high-risk populations. Although randomized controlled trials evaluating screening and treatment outcomes are lacking, experts support routine screening for AIN in high risk populations. Screening is performed using anal cytological exams, similar to those performed in cervical cancer screening programs, along with direct tissue evaluation and biopsy via high resolution anoscopy. AIN can be treated using topical therapies such as imiquimod, 5-flurouracil, and trichloroacetic acid, as well as ablative therapies such as electrocautery and laser therapy. Reductions in AIN and anal cancer rates have been shown in studies where high-risk populations were vaccinated against the oncogenic strains of HPV. Currently, the CDC recommends both high-risk and average-risk populations be vaccinated against HPV infection using the quadrivalent or nonavalent vaccines. It is important for clinicians to be familiar with AIN and the role of HPV vaccination, particularly in high risk populations.

Keywords: Anal cancer; Anal intraepithelial neoplasia; Anal squamous cell carcinoma; Human papillomavirus vaccine; Human papillomavirus

Core tip: Anal intraepithelial neoplasia (AIN) is the precursor lesion to anal squamous cell carcinoma. AIN incidence is low in the general population, but rivals colon cancer in high risk groups, particularly those with human immunodeficiency virus infection and men who have sex with men. Thus, screening for AIN and early anal cancer and treatment of these lesions at expert centers should be considered in high risk populations. Screening is performed using anal cytology and high resolution anoscopy, and treatment consists of either topical or ablative therapies. Finally, human papillomavirus vaccination appears to reduce the rate of AIN and possibly anal cancer.