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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 ß-carotene and 25,000 IU of retinyl palmitate in 18,314 persons at high risk for lung cancer. We studied two high-risk populations: 4,060 men with extensive occupational exposure to asbestos, and 7,965 men and 6,289 women with at least 20 pack-years of cigarette smoking history. CARET began in 1985 with two pilot studies and expanded to six sites beginning in 1988. The CARET 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 (NEJM 334:1150-5, 1996; JNCI 88:1550-9, 1996). Lung cancer incidence and cardiovascular disease mortality findings during the first six years of post-intervention follow-up were published in 2004 (JNCI 96:1743-50, 2004). As of June 30, 2005, CARET stopped active follow-up of CARET participants. CARET, supported by an NCI grant led by PI Dr. Chu Chen, continues to support the extensive biological repository and ancillary studies that utilize the CARET samples and data.