• National Cancer Institute, Division of Cancer Control and Population Sciences, 9609 Medical Center Dr, Room 4E-608, Bethesda, MD 20892-9763, USA. Electronic address: marcusp@mail.nih.gov.
• Colorado Colorectal Screening Program, University of Colorado Cancer Center, University of Colorado Anschutz Medical Campus, 13001 E 17th Pl, Aurora, CO 80045, USA. Electronic address: Sheryl.ogden@ucdenver.edu.
• University of Utah, Department of Family and Preventive Medicine, 375 Chipeta Way, Salt Lake City, UT 84108, USA. Electronic address: Lisa.gren@hsc.utah.edu.
• University of Utah, Division of Oncology, 2000 Circle of Hope, Room LL376, Salt Lake City, UT 84112, USA. Electronic address: jeff.childs@hsc.utah.edu.
• University of Colorado Anschutz Medical Campus, 13001 E 17th Pl, Aurora, CO 80045, USA. Electronic address: Shannon.pretzel@ucdenver.edu.
• Department of Public Health Sciences, Henry Ford Health System, 1 Ford Place, Detroit, MI 48202, USA. Electronic address: llamera1@hfhs.org.
• Harvard Medical School, 180 Longwood Ave, Boston, MA 02115, USA. Electronic address: walsh@hcp.med.harvard.edu.
• National Cancer Institute, Division of Cancer Control and Population Sciences, 9609 Medical Center Dr, Room 4E-608, Bethesda, MD 20892-9763, USA; Drexel University School of Public Health, 1505 Race St., Philadelphia, PA 19102, USA. Electronic address: heather.rozjabek@gmail.com.
• Information Management Systems, 6110 Executive Blvd, Rockville, MD 20852, USA. Electronic address: mabiej@imsweb.com.
• Information Management Systems, 6110 Executive Blvd, Rockville, MD 20852, USA. Electronic address: thomasb@imsweb.com.

OBJECTIVE: Identify predictors of non-compliance with first round screening exams in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial.

METHOD: The PLCO was conducted from 1993 to 2011 at 10 US institutions. A total of 154,897 healthy men and women ages 55-74 years were randomized. Intervention arm participants were invited to receive gender-appropriate screening exams for prostate, lung, colorectal and ovarian cancer. Using intervention-arm data (73,036 participants), non-compliance percentages for 13 covariates were calculated, as were unadjusted and adjusted odds ratios (ORs), and 95% confidence intervals. Covariates included demographic factors as well as factors specific to PLCO (e.g., method of consent, distance from screening center).

RESULTS: The rate of non-compliance was 11% overall but varied by screening center. Significant associations were observed for most covariates but indicated modest increases or decreases in odds. An exception was the use of a two-step consent process (consented intervention arm participants for exams after randomization) relative to a one-step process (consented all participants prior to randomization) (OR: 2.2, 95% CI: 2.0-2.5). Non-compliance percentages increased with further distance from screening centers, but ORs were not significantly different from 1.

CONCLUSIONS: Many factors modestly influenced compliance. Consent process was the strongest predictor of compliance.