Over the past year, major attention has focused on whether cancer arises by chance or as a result of external factors that, if modifiable, could imply that cancer is preventable and not simply the result of random events. The underlying truth of this debate has major implications for everything from the Vice President’s Moonshot1—are we preventing cancer or only aiming to treat it after it develops?—all the way to policies and practices that may determine cancer risk for future generations.