To provide support for centralized follow-up of participants from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. PLCO is designed to determine if screening for prostate, lung, colorectal and ovarian cancer can reduce mortality from these cancers. In addition, PLCO has a collection of pre- and post-diagnostic biological samples stored in the PLCO Biorepostory, and epidemiological data from questionnaires. These data are a valuable resource for cutting-edge molecular epidemiologic research.