The Carotene and Retinol Efficacy Trial (CARET) was a randomized, double-blind, placebo-controlled trial of the cancer prevention efficacy and safety of a daily combination of 30 mg of beta-carotene and 25,000 IU of retinyl palmitate in 18,314 persons at high risk for lung cancer. CARET began in 1985, and the intervention was halted in January 1996, 21 months ahead of schedule, with the twin conclusions for definitive evidence of no benefit and substantial evidence of a harmful effect of the intervention on both lung cancer incidence and total mortality. CARET continued to follow and collect endpoints on their participants through 2005. During the active intervention phase of CARET, serum, plasma, whole blood, and lung tissue specimens were collected on participants. These biospecimens make up the CARET Biorepository.

The CARET Biorepository is a valuable resource for population-based studies of the major human cancers. During CARET's twenty years of follow-up (1985-2005), we have received reports of 1,445 participants with lung cancer, 901 with prostate cancer, 433 with breast cancer, 334 with bladder cancer, 332 with colon cancer, and 1,429 with other cancers. CARET is one of the few trials that has prospectively collected serum, plasma, whole blood, blood spots (for DNA), and lung cancer tumor specimens, as well as smoking history and serial food frequency questionnaires (in some individuals for up to 12 years) in populations at high risk for lung cancer. This wealth of information in over 18,000 individuals makes the CARET Biorepository a special resource for cancer researchers.