EFFECTS OF 2 DIETARY-FAT LEVELS AND 4 DIETARY LINOLEIC-ACID LEVELS ONMAMMARY-TUMOR DEVELOPMENT IN BALB C-MMTV MICE UNDER AD-LIBITUM FEEDING CONDITIONS/

The relationship between dietary fat intake (level and type) and the d evelopment of breast cancer in humans is a matter of concern in Wester n society. A high fat intake is associated with a greater mammary canc er risk in humans and in animal models. Higher intake of polyunsaturat ed fatty acids in humans shows little or no association with mammary t umor development in epidemiologic surveys. From literature data, it ap pears that a higher intake of polyunsaturated fatty acids (linoleic ac id) is related to an increase in mammary tumorigenesis in animal studi es in which chemical carcinogens like dimethylbenz[a]anthracene are us ed as tumor initiator. Mostly the latency period in these chemically i nduced models is rather short. In this study, the Balb/c-MMTV (mouse m ammary tumor virus) mouse strain was chosen as an animal model: MMTV l eads to turner initiation, and dietary factors influence tumor promoti on over a relatively long latency period. The mice were fed diets with two fat concentrations: a high [36% of energy (en%)] or low (16 en%) fat level; fat was isocalorically replaced by carbohydrates (cornstarc h). At both dietary fat levels, linoleic acid was given at four levels : 2, 3, 6, and 10 en%. Linoleic acid-rich fat was isocalorically repla ced by oleic acid-rich fat. The diets were consumed an libitum over a lifetime. Animals were euthanized as soon as mammary turner diameter w as greater than or equal to 1 cm or when the animals were in a poor cl inical condition. The incidence of mammary tumors at 18 months was sig nificantly higher in one group only: 36 en% fat and 2 en% linoleic aci d. This group also showed the shortest mean latency period for mammary tumor development. Mean mammary tumor incidence was higher and mean o nset time shorter in the four high-fat groups than in the low-fat grou ps. No (linear) close-response relationship between dietary linoleic a cid concentration and mammary tumor incidence and latency period was o bserved. This indicates that a higher dietary linoleic acid intake doe s not increase the incidence or shorten the latency period of breast c ancer in the Balb/c-MMTV mouse strain at two different dietary fat lev els.