ANAL INTRAEPITHELIAL NEOPLASIA

ANAL INTRAEPITHELIAL NEOPLASIA

AIN is a multifocal virally induced dysplasia of the perianal or intra-anal epidermis associated with HPV . Subtypes 6 and 11 are most often associated with warts and early AIN, whereas subtypes 16 and 18 account for more than 75% of anal cancers. The prevalence is <1% of the population with a rising incidence, especially in those areas where ano-receptive inter course and HIV are prevalent. At-risk groups include patients with HIV as well as immunocompromised patients, women with a history of other genital intraepithelial neoplasia (VIN and CIN) and pa tients with extensive anogenital condylomata. Patients may be asymptomatic and the diagnosis is often a histological surprise, although increasing numbers in high-risk groups are picked up on anal cytology . It is classified according to the degree of dysplasia on biopsy into AIN /uni00A0 I, AIN /uni00A0 II and AIN /uni00A0 III, according to the lack of keratocyte maturation and extension of the proliferative zone from the lower third (AIN /uni00A0 I) to the full thickness of the epithelium (AIN /uni00A0 III), in the same manner as cervical or vulval dysplasia. The natural history is uncertain but progression from AIN /uni00A0 II to AIN /uni00A0 III to invasive carcinoma has been observed, notably in the immunocompro mised. The term Bowen’s disease is no longer used.