At least 35 in-vitro studies have reported that selenium produces cytotoxic effects on a variety of cancer cell lines.1-5, b At least 20 studies have reported that sele nium produced antitumor effects in animals.
a ^s in all sections of Part III with this heading, the information summarized was obtained primarily from the MEDLINE database; papers not indexed in MEDLINE are generally not included. The summaries are only for studies conducted with cancer cells; mechanistic studies not involving cancer cells (such as those on PTK inhibition, for example) are not summarized. Lastly, these summaries focus on studies pertinent to cancer treatment, not prevention.
b In all of Part III, if more than about seven studies demonstrated a particular effect, usually only about five will be listed as references; to list more would be too cumbersome. Those listed serve as examples that support the point.
c Technically, the term antitumor refers to a reduction in tumor volume in animals, whereas anticancer refers to the same in humans. To avoid awkward sentences, I use the two phrases interchangeably, and use both phrases in their broadest sense to refer not only to tumor regression but also to antiangiogenesis, anti-
man anticancer trials have not yet been conducted, other than one in which selenium was used in the symptomatic treatment of brain tumor patients.12 In that trial, selenium, in combination with several other therapeutic agents, produced general improvements such as reductions in nausea and headaches. Still other studies have reported that selenium reduced the side effects of chemotherapy drugs; these are discussed in Chapter 23.
Apart from cancer treatment studies, a number of human trials have reported that selenium supplementation could reduce the risk of developing cancer.13-17 Other large human cancer prevention trials are now in progress. Many animal studies also have reported that sele-
nium may reduce cancer risk.
In addition to the above studies on supplementation, some epidemiologi-cal studies have reported that low dietary intake of selenium is associated with increased risk of several cancers, although the results of the epidemiologic studies as a whole are inconsistent.
In total, the studies on selenium suggest that supplementation may be useful in both cancer prevention and treatment. Although most human studies thus far have looked at its preventive effects, numerous animal studies have suggested selenium may be useful in treating established cancers. The results from in-vitro studies support its potential as an anticancer compound.
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