In 1993, the National Cancer Institute launched one of the largest cancer screening trials ever planned in the United States, in an effort to answer the question of screening efficacy in four cancers: prostate, lung, colorectal, and ovarian. Ten centers across the country ultimately accrued more than 150,000 men and women for this study. Nineteen years after it began, PLCO has now released the trial’s final major outcome finding, for colorectal cancer.