KLK3 and prostate cancer: Positive associations were also replicated in two updated nested case-control studies: one from the Alpha-Tocopherol-Beta-Carotene trial which investigated the use of α-tocopherol and β-carotene supplements among smokers, and one from the placebo arm of the Prostate Cancer Prevention Trial (PCPT) which examined the effect of prostate-specific antigen screening for prostate cancer in healthy adult men [23,24,25].