Subjects in the screening group of the PLCO Cancer Screening Trial had undergone testing for the detection of prostate cancer (the prostate-specific antigen [PSA] test and digital rectal examination), lung cancer (chest radiography), colorectal cancer (sigmoidoscopy), and ovarian cancer (the CA-125 test and transvaginal ultrasonography). Subjects who provided annual blood samples for 6 years for the PSA test (in men) or CA-125 (in women) were also asked to contribute additional blood samples for research on cancer and other diseases common to their age group. In addition, information on incident cancers (type and date) was obtained prospectively with the use of standardized questionnaires that were mailed to all study subjects annually. Trained PLCO data abstracters reviewed and confirmed each reported case of cancer.
