Cidofovir could be an effective drug for the treatment of Anal Intraepithelial Neoplasia(AIN).

• Inclusion Criteria:

  1. Patients who have given informed consent in writing of the study before making any specific selection procedure for the study.
  2. Adult patients (18 years) with documented HIV infection, with high-grade AIN demonstrated by biopsy, and have not received any prior treatment for Anal Intraepithelial Neoplasia in the last 12 weeks.
  3. For women of childbearing potential, negative pregnancy test in urine screening visit. All women of childbearing age should continue effective contraception throughout the study treatment.

• Exclusion Criteria:

  1. Patients who have received previous treatment of Anal Intraepithelial Neoplasia (AIN) in the last 12 weeks. 2. Dermatoses in patients with anogenital area 3. Patients with a history of pre-invasive neoplasia associated with Human Papilloma Virus 4. Patients with a history of previous neoplasm, of any origin and location, in the past 5 years.

  5. Patients with a history of hematologic abnormalities, kidney or liver 6. Pregnant or breastfeeding women or women of childbearing age who do not wish to use adequate contraception at the discretion of the investigator.

  7. Any disease or condition of the patient which, in the opinion of the investigator, is not adequate patient participation in the study.