A large cohort study of etiologic determinants of cancer was carried out within an NCI trial for the evaluation of screening procedures for the early detection of prostate, lung, colon, and ovarian cancer (the PLCO Trial) at 10 U.S. screening centers. The 74,000 screening arm participants in the trial were examined over a four-year period and then followed for cancer occurrence for an additional 10 years through annual follow-up mailings. At each screening examination, biologic samples were collected. Because of the prospective design, screening examinations, and sequential pre-diagnostic blood sample collections, it is possible to relate temporal changes in biomarkers to the development of cancer in this cohort. Initial studies focused on genetic and environmental determinants of adenomatous polyps and colorectal cancer.
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