Considerations in the design of studies of dietary influences on mammary carcinogenesis in rats and mice

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Animal models of breast cancer: experimental design and their use in nutrition and psychosocial research

This is the second Special Issue addressing the diversity and use of animal models of breast cancer. The previous issue (Breast Cancer Res Treat 39:1-135, 1996), dealt with a variety of topics such as the characteristics of chemically- and virally-induced rodent models, immunobiologies of immunedeficient mice, transgenic mouse models, and models of metastasis. In the first part of this second Special Issue, the articles address animal models for studying life-style factors, including psychosocial, exercise, and nutritional research in breast cancer. In the second section, there is emphasis on the controversial area of dietary fat, with other authors addressing caloric restriction and dietary isoflavonoids, retinoids, and monoterpenes in the third part. In the final section, a series of authors provide suggestions for approaching various issues involving experimental design, including nutritional studies, drug screening models, statistical considerations, quantitation of tumor growth kinetics, and animal husbandry. These articles, and some additional issues raised during the previous Special Issue, are briefly discussed in this overview. They include a further evaluation of the relative merits of 7,12-dimethylbenz(a)anthracene and N-nitroso-N-methylurea as carcinogens, and of the use of the AIN76 and AIN93 semipurified diets in studies of mammary carcinogenesis.