To compare the effectiveness of two application schemes of cryosurgery during a 5 week course of topical imiquimod i.e. cryosurgery at the end of the second week of imiquimod followed by 3 more weeks of imiquimod (immunocryosurgery) versus cryosurgery at day 0 followed by 5 weeks of topical imiquimod (cryoimmunotherapy)