In a late-stage clinical trial, Merck's investigational quadrivalent human papillomavirus (HPV) vaccine, Gardasil, showed the vaccine is capable of preventing 100% of high-grade cervical precancers known as cervical intraepithelial neoplasia (CIN) as well as noninvasive cervical cancers, such as adenocarcinoma in situ (AIS), associated with HPV types 16 and 18. More than 12,000 women between the ages of 16 and 26 participated in the prospective, randomized, double-blind, placebo-controlled study, know as Future II.