Anal cancer rates are rising in the United States. A recent analysis found that new cases rose by 2.7% and deaths increased by 3.1% between 2001 and 2016. Anal cancer is caused by human papillomavirus (HPV). HPV vaccination can prevent it, and anal Pap smears can detect precancerous cell changes, known as dysplasia, before they progress to invasive cancer. A recent Spanish study of more than 3,000 people with HIV showed that annual screening followed by prompt treatment reduced the likelihood of an anal cancer diagnosis by 83%. But such screening is not routinely performed, and it is not yet clear what ought to be done with the results. Another study of gay and bisexual men found that while high-grade dysplasia is common, it often does not progress to cancer, suggesting that routine treatment might not be necessary. The ANCHOR study is testing whether immediate treatment of precancerous cell changes could reduce the risk of developing anal cancer.