Inclusion Criteria:

To be included in the cohort, patients have to:

- have an anal AIN3 (including Bowen's disease) diagnosed by histology (screening
population, post-operative discovery…)

- Aposteriori for patients with a history of anal AIN3 complicated or not by an anal
cancer. These cases will be identified from data bases of anatomopathology
laboratories in hospitals since January 1st 2000.

- At the diagnostic for the new anal AIN3 Units care involved in the study are those
involved in the follow-up of patients with anal pathologies en France, especially
anal cancer. Samples are analyzed by the laboratories of anatomopathology of the
hospitals where the patients are diagnosed. These points make the histological data
bases reliable and allow clearly identifying cases of anal ain3 retrospectively since
2000.

Taking in account the number and quality of the units care involved in the study and the
way cases are identified, we think our recruitment will be exhaustive in France, to limit
selection bias.

- Patient's non opposition to study

Exclusion Criteria:

- history of anal carcinoma without any history of anal AIN3 lesion

- impossible follow-up for the duration of the study (3 years or more)

- patient aged under 18