The primary objective of this project is to determine whether selenium supplementation affects candidate markers of breast cancer risk in a cohort of women at elevated risk for breast cancer. The intermediate biomarkers to be studied are: indicators of oxidative damage to cellular macromolecules such as DNA and lipid, indicators of IGF metabolic status, and cellular indicators of breast cancer risk. We propose a randomized, placebo-controlled, double-blind chemoprevention trial with 150 participants (75 subjects per arm) using a placebo tablet or a tablet containing 200 µg high-selenium brewer’s yeast per day, given for a duration of one year. The form and dose of selenium that will be used has been reported to reduce cancer incidence and mortality in lung, prostate, and colon. Blood and urine will be collected at baseline, and after 6 and 12 months of intervention. Breast epithelial cells/tissue will be obtained via nipple aspiration or fine needle aspiration at baseline and the end of the intervention. Plasma selenium and glutathione peroxidase activity will be assessed in addition to pill counts and self report as markers of compliance. Our specific aims are stated in the following questions.

Does selenium supplementation inhibit the oxidation of cellular macromolecules? We will assess the effects of selenium on several oxidative markers. These markers include 8-hydroxydeoxyguanosine (8-OHdG) in DNA of lymphocytes isolated from blood and in urine, malondialdehyde and 8-iso-prostaglandin F2 -alpha (8-EPG) in plasma and urine. Levels of these indices will be determined at baseline and after 6 and 12 months of selenium supplementation. In addition, we will evaluate the feasibility of determining the degree of cellular DNA damage in breast epithelial cells from nipple aspirate fluid or fine needle aspirates of the breast using the comet assay (in the presence and absence of endonuclease III or FPG), a single cell gel electrophoresis assay that detects DNA strand breaks as well as oxidative damage to purines and pyrimidines.

Does selenium supplementation decrease circulating levels of IGF-1 and/or IGFBP-3? A growing number of reports hypothesize that IGF-1 and its binding protein, IGFBP-3, can be used as surrogate biomarkers for cancer risk; good evidence exists to support this hypothesis relative to breast cancer risk. Moreover, some selenium compounds have been shown to alter circulating levels of IGF-1 and IGFBP-3 in a manner consistent with a reduced risk for cancer. Reported effects on levels and/or metabolism of IGF-1 and IGF-BP-3 are consistent with our finding that selenium induces apoptosis as well as with the finding of Lu and coworkers that selenium may act by inhibiting angiogenesis. Initially, we will study the effect of selenium on circulating levels of IGF-1 and IGFBP-3.

Does selenium supplementation alter characteristics of breast epithelial cells that reflect a change in their pathological status and/or potential for promotion and progression? Clinical evidence indicates that field cancerization effects occur during malignant transformation, and that changes in the disease process may be reflected in these fields of cells. Thus, if selenium were exerting a beneficial effect(s) on the carcinogenic process, it would be expected that such an effect(s) could be detected in fields of cells of the target tissue. To pursue this hypothesis, we will conduct a feasibility study in which breast epithelial cells will be obtained via nipple aspiration or fine needle aspiration. Samples will be collected at baseline and again at the end of the study. In the samples obtained, we will determine whether selenium alters the percentage of abnormal cells identified by changes in their nuclear morphometry using a CAS 200 computer-assisted image analysis system to collect morphometric data.

Currently, there are inadequate biomarkers by which to track changes in breast cancer risk, and there is no information about which candidate markers that selenium supplementation modifies. Ultimately this type of information is essential to selecting the optimal form and dose of selenium to choose for clinical studies of selenium chemoprevention in which cancer incidence is the endpoint. The study proposed has the potential to identify surrogate endpoint biomarkers that selenium supplementation modulates, and that can be used to monitor the effectiveness of selenium in the chemoprevention of breast cancer.