What Is the Risk of Anal Carcinoma in Patients With Anal Intraepithelial Neoplasia III?

BACKGROUND: The risk of anal carcinoma after previous diagnosis of anal intraepithelial neoplasia III is unclear. OBJECTIVE: The purpose of this study was to estimate the risk of anal carcinoma in patients with anal intraepithelial neoplasia III and to identify predictors for subsequent malignancy. DESIGN: This was a retrospective review using the Surveillance, Epidemiology, and End Results registry (1973-2014). SETTING: The study was composed of population-based cancer registries from the United States. PATIENTS: Patients who were diagnosed with anal intraepithelial neoplasia III were included. MAIN OUTCOME MEASURES: The primary outcome was rate of subsequent anal squamous cell carcinoma. Predictors for anal cancer were identified using logistic regression and Cox proportional hazard models. RESULTS: A total of 2074 patients with anal intraepithelial neoplasia III were identified and followed for a median time of 4.0 years (interquartile range, 1.8-6.7 y). Of the cohort, 171 patients (8.2%) subsequently developed anal cancer. Median time from anal intraepithelial neoplasia III diagnosis to anal cancer diagnosis was 2.7 years (interquartile range, 1.1-4.5 y). Fifty-two patients (30.4%) who developed anal carcinoma were staged T2 or higher. Ablative therapies for initial anal intraepithelial neoplasia III were associated with a reduction in the risk of anal cancer (OR = 0.3 (95% CI, 0.1-0.7); p = 0.004). Time-to-event analysis revealed that the 5-year incidence of anal carcinoma after anal intraepithelial neoplasia III was 9.5% or approximate to 1.9% per year. LIMITATIONS: The registry did not record HIV status, surveillance schedule, use of high-resolution anoscopy, or provider specialty. CONCLUSIONS: In the largest published cohort of patients with anal intraepithelial neoplasia III, approximate to 10% of patients were projected to develop anal cancer within 5 years. Nearly one third of anal cancers were diagnosed at stage T2 or higher despite a previous diagnosis of anal intraepithelial neoplasia III. Ablative procedures were associated with a decreased risk of cancer. This study highlights the considerable rate of malignancy in patients with anal intraepithelial neoplasia III and the need for effective therapies and surveillance. See Video Abstract at http://links.lww.com/DCR/A764.