Canadian National Breast Screening Study

Carotenoids and breast cancer — Among seven case-control studies investigating the correlation between different carotenoid plasma levels or dietary intakes and breast cancer risk, five showed significant inverse associations with some carotenoids. - In most cases, this protective effect was due to 3-carotene and lutein. However, one (the Canadian National Breast Screening Study ) showed no association for all studied carotenoids including (I-carotene and lutein. More recently, another study even demonstrated a positive correlation between breast cancer risk and tissue and serum levels of P-carotenes and total carotenes. Nevertheless, these observational results must be confirmed by intervention studies to prove consistent. 

Boyd NF, Byng JW, Jong RA, et al. Quantitative classification of mammographic densities and breast cancer risk Results from the Canadian National Breast Cancer Screening Study. J Natl Cancer Inst 1995 87 670-675. 

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