Carcinogenesis in the Mammary Gland

Colon cancer can be induced in mice and rats by irradiation (UNSCEAR, 1977) and a number of chemical carcinogens, induding 

Systemic administration of colonic carcinogois yields the entire spectrum of changes seen in human colon cancer, including abnormal crypt architecture with disrupted proliferation, papillary and adenomatous polyps, carcinoma in situ, and adenocarcinoma (Thumherr et al., 1973). The distal colon is affected with the greatest frequency, and squamous cell canc of the anus is also produced. Dietary fat enhances the production of colonic tumors (Nigro et al., 1975), perhaps by increasing bile flow (Narisawa et al., 1974). 

Irradiation induces leukemias and lymphomas of varying types and frequencies in laboratory animals, depending on the conditions of irradiation and the susceptibility of the exposed species and strain (Upton, 1967 Kaplan, 1967 UNSCEAR, 1977). Similarly, such neoplasms are induced by various chemicals, e.g., 3-methylcholanthrene (Irino et al., 1968 Akamatsu et al, 1968), estrogens (Gardner and Dough ty, 1944), 7-12-dimethylbenzanthracene (Sydnor et al., 1962 Huggins and 

Sugiyama, 1966), 4-nitroquinoline-l axide (Nishizuka et al., 1964), N-nitrosobutylurea (Odashima, 1969, 1970 Yokoro et al., 1970), myleran (Upton et al., 1961), nitrogen mustard (Conklin et al., 1963), 1-atoyI-l-nitrosourea (Ogiu, 1978), and benzene (Snyder et al., 1980, Maltoni et al., 1983 Cronkite etal., 1984). 

Retroviruses have been isolated repeatedly from radiation-induced and chemically induced leukemias however, their role, if any, in the induction of these neoplasms remains uncertain at this time (Kaplan, 1984). 

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Alpha-tocopherol has been shown to be useful in the prevention of nitrosation in non-aqueous systems (20,22). Additionally, carcinogenesis by preformed carcinogens has been inhibited by alpha-tocopherol, as is shown in Table IV. Interestingly, 7,12-dlmethyl-benz(a)anthracene (DMBA)-lnduced carcinogenesis in the mammary gland was inhibited only in rats fed high fat or high selenium levels with the vitamin E supplement (23,24). 

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