Intraepithelial neoplasia in the anal canal. The appearance and relation to genital neoplasia.

Anal canal intraepithelial neoplasia (ACIN) in the form of squamous dysplasia and carcinoma in situ is a rare condition. In this paper we present all 19 cases diagnosed in Denmark in a two-year period. The incidence was 0.2/10(5)/year compared to 0.7/10(5)/year for variants of squamous carcinoma in the anal canal. Most cases of ACIN were incidental findings at minor anal surgery. Histologically, one half of the lesions were located in the anal transitional zone above the dentate line. Two of the 19 patients died from colo-rectal carcinoma and 17 were alive 5 years later. Nine of the patients were controlled by biopting, and 4 recurrences of the intraepithelial changes were found among these, all with an initial lesion of ACIN III. None of the patients developed invasive carcinoma of the anal canal during the 5 years, but one half of the females had previous or accompanying neoplasia of the vulva and perineum.