• Division of Cancer Prevention, National Cancer Institute, Bethesda, MD 20892, USA. pp2g@nih.gov

The most rigorous and valid approach to evaluating cancer screening modalities is the randomized controlled trial (RCT). RCTs are major undertakings and the intricacies of trial design, operations, and management are generally underappreciated by the typical researcher. The purpose of this article is to inform the reader of the "nuts and bolts" of designing and conducting cancer screening RCTs. Following a brief introduction as to why RCTs are critical in evaluating screening modalities, we discuss design considerations, including the choice of design type and duration of follow-up. We next present an approach to sample-size calculations. We then discuss aspects of trial implementation, including recruitment, randomization, and data management. A discussion of commonly employed data analyses comes next, and includes methods for the primary analysis (comparison of cause-specific mortality rates between the screened and control arms for the cancer of interest), as well as for secondary endpoints such as sensitivity. We follow with a discussion of sequential monitoring and interim analysis techniques, which are used to examine the primary outcome while the trial is ongoing. We close with thoughts on lessons learned from past cancer screening RCTs and provide recommendations for future trials. Throughout the presentation we illustrate topics with examples from completed or ongoing RCTs, including the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial and the National Lung Screening Trial (NLST).