Selenium (Se) is a ubiquitous, albeit not uniformly distributed metalloid present in earth crust.
Consequently, its human intake with food products, particularly grains and vegetables, is also very uneven, and in
certain cases can result in a severe Se deficiency. It was also documented that Se deficiency observed in some
countries and/or geographic regions (e.g. Keshan region in China), is associated with an increased morbidity and
mortality of neoplastic diseases. To correct this problem a number of organic and inorganic selenium compounds were
developed and tested. However, it is now firmly established that only an inorganic sodium selenite with four-valent Se,
and not that with six-valent (selenate) cation shows anticancer activity. This difference in their biological activities is
due to their physicochemical properties. Thus selenite (Se+4) can undergo redox reaction, for example with protein’s
sulfhydryl groups expressed on the surface of tumor cells. In this way selenite prevents non-enzymatic formation of
parafibrin that coats tumors cells and hence presents them as ‘self’ to the innate cellular immune system. Consequently,
macrophages of the lymphatic system do not recognize neoplastic cells as ‘foreign‘ bodies and spare them from the
immune destruction. This mechanism can explain the failure of various immunotherapies to completely eliminate
tumors from human bodies. Another contributing factor to carcinogenesis is the excessive consumption of red meat
containing redox-active iron (Fe+3) that initiates parafibrin formation from blood fibrinogen. In conclusion, sodium
selenite is a readily available and inexpensive drug of choice in the cancer treatment and prevention.