Malignant transformation of high-grade anal intraepithelial neoplasia

Background: The natural history of anal intraepithelial neoplasia (AIN) is uncertain. This makes management problematic as treatment options to eradicate the condition carry morbidity. The authors report their 10-year experience with conservative management of this condition, highlighting the lessons learnt. Methods: All patients were diagnosed with high-grade AIN (AIN III) between 1994 and 2003. Diagnosis was by full-thickness biopsy and histopathological examination. Excision of localized lesions was undertaken, and all patients underwent follow-up every 6 months. Prospective data were collected regarding recurrence, postoperative complications and progression to invasive carcinoma. Results: Thirty-five patients were followed for a median of 63 (range 14-120) months. Excision of localized high-grade AIN was carried out in 28 patients with minimal morbidity. Six patients were systemically immunosuppressed at diagnosis, all of whom had multifocal perianal lesions. Three immunosuppressed patients developed invasive anal squamous carcinoma during follow-up. By contrast, no invasive carcinomas were identified among immunocompetent patients with either localized or multifocal perianal disease. Conclusion: AIN III appears to have a relatively low potential for malignant transformation in the immunocompetent patient. However, immunosuppressed patients are more likely to have extensive AIN III and a greater risk of malignant change.