at least in mice, playing with selenium supplements may be playing with fire!

[Lani]

Int J Cancer. 2013 Apr 23. doi: 10.1002/ijc.28224. [Epub ahead of print]
Dietary selenium supplementation modifies breast tumor growth and metastasis.
Chen YC, Prabhu KS, Das A, Mastro AM.
Source
The Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802.
Abstract
The survival rate for breast cancer drops dramatically once the disease progresses to the metastatic stage. Selenium (Se) is an essential micronutrient credited with having high anti-cancer and chemopreventive properties. In this study, we investigated if dietary Se supplementation modified breast cancer development in vivo. Three diets supplemented with sodium selenite, methylseleninic acid (MSA) or selenomethionine (SeMet), as well as a Se-deficient and a Se-adequate diet were fed to mice before mammary gland inoculation of 4T1.2 cells. The primary tumor growth, the numbers of cancer cells present in lungs, hearts, livers, kidneys, and femurs and several pro-inflammatory cytokines were measured. We found that inorganic selenite supplementation provided only short-term delay of tumor growth while the two organic SeMet and MSA supplements provided more potent growth inhibition. These diets also affected cancer metastasis differently. Mice fed selenite developed the most extensive metastasis, and had an increased incidence of kidney and bone metastasis. On the other hand, mice fed the SeMet diet showed the least amount of cancer growth at metastatic sites. The MSA diet also provided some protection against breast cancer metastasis although the effects were less significant than those of SeMet. The cytokine profiles indicated that serum levels of IL-2, IL-6, IFNγ, and VEGF were elevated in SeMet-supplemented mice. There was no significant difference in tumor growth and the patterns of metastasis between the Se-deficient and Se-adequate groups. Our data suggest that organic Se supplementation may reduce/delay breast cancer metastasis while selenite may exacerbate it. © 2013 Wiley Periodicals, Inc.
Copyright © 2013 UICC.
PMID: 23613334 [PubMed - as supplied by publisher]