Figure. Study flow diagram.

Studies not shown but included were acetylsalicylic acid (ASA) studies or studies that considered more than 1 intervention, outcome, or both. The Nurses' Health Study (NHS) represents an initial publication (46) and a follow-up publication (34) for colorectal cancer (CRC) and a separate publication for colorectal adenoma (CRA) (47). Three cyclooxygenase (COX)-2 inhibitor polyp studies and a systematic review were added after we submitted our report to the U.S. Preventive Services Task Force and the Agency for Health Research and Quality. *11 of these considered harms of ASA. CV = cardiovascular; NSAID = nonsteroidal anti-inflammatory drug; RCT = randomized, controlled trial.