Sunday Nov 17, 2013 (foodconsumer.org) -- An animal study in International Journal of Cancer suggests that supplementation with selenium compounds may help prevent or delay the progression or metastatisis of breast cancer.  But some may actually worsen the progression.

Y. C. Chen and colleagues from The Pennsylvania State University in University Park, Pennsylvania conducted the study and found organic selenium supplements worked better than inorganic selenium supplements in preventing growth of cancer in metastatic sites in mice although none of them could 100% stop the disease.

For the study,  diets 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 4T1.2 cells were injected into mammary glands.  4T1.2 is a clonal cell line derived from the mouse breast cancer cell line 4T1.  After inoculation, the primary tumor growth in mammary glands, and the numbers of cancer cells in the lungs, heart and kidneys were counted.

As a result, sodium selenite were found only to provide short term delay of tumor growth while methylseleninic acid and selenomethionine supplements rendered more powerful growth inhibition of the primary tumors in mammary gland (or breast cancer).

Mice treated with sodium selenite diet actually increased incidence of kidney and bone metastasis and mice treated with the selenomethionine diet had the least amount of cancer growth at metastatic sites.  And methylseleninic acid had a moderate protective effect against breast cancer metastasis but its protection was less significant, compared to that of selenomethionine.

No difference in tumor growth and patterns of metastasis between selenium sufficient diet and selenium deficient diet.

The study concluded "organic Se supplementation may reduce/delay breast cancer metastasis, while selenite may exacerbate it." (David Liu, PHD)