The Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial was a large randomized controlled trial that assessed whether certain screening practices decreased deaths from prostate, lung, colorectal and ovarian cancer. Approximately 155,000 men and women aged 55 to 74 years old were enrolled from 10 screening centers across the United States between November 1993 and July 2001. Participants were followed for 13 years after the randomization visit.

The following screening methods were assessed:

• Prostate cancer: digital rectal examination (DRE) and a serum prostate-specific antigen (PSA) test
• Lung cancer: chest x-ray
• Colorectal cancer: flexible sigmoidoscopy
• Ovarian cancer: CA125 and transvaginal ultrasound (TVU)

Exclusion criteria were as follows:

• Less than 55 or greater than 74 years of age. (Prior to January 1996, the age of eligibility was 60 years of age.)
• Prior diagnosis of prostate, lung, colorectal or ovarian cancer.
• Ongoing treatment for any cancer except basal or squamous cell skin cancer.
• Participation in another cancer screening or primary prevention trial.
• Men who took Proscar/Propecia/finasteride within 6 months prior to randomization.
• Women who took Tamoxifen or Evista/Raloxifene within 6 months prior to randomization. (No longer an exclusion criteria as of April 1999.)
• Prior surgical removal of the entire prostate, entire colon, one lung, or both ovaries. (Beginning in October 1996, women with oophorectomies were no longer excluded.)
• Starting in April 1995: males with more than one prostate specific antigen (PSA) test within the last three years.
• Starting in April 1995: participants with a colonoscopy, sigmoidoscopy, or barium enema within the last three years.

Data was collected through medical records, lab results, images, death certificates, self-administered questionnaires, and biospecimens. Cancer data was collected up to December 31, 2009 while mortality data was collected through 2015.