Topical Imiquimod 5% Cream for Treatment of Cutaneous Neurofibromas in Adults With Neurofibromatosis 1

* Three of the participant's tumors will be treated with imiquimod cream and one tumor (out of all the remaining tumors) will be followed without treatment (control tumor). * Participants will be given a tube of imiquimod cream and be asked to apply it to the three tumors 5 times per week, for a full 6 weeks (Monday through Friday). * Participants will be required to come to the hospital for examinations on Week 1, 2, 4 and 6 (+/- 3 calendar days) and after their last dose of imiquimod cream on Weeks 9, 12 and 18 (+/- 5 calendar days. The following tests and procedures will be performed: skin test; vital signs and measurements and photographs of the tumors. Participants will be asked to participate in an optional skin biopsy on Week 4 and research blood tests wil lbe taken on Day 1.