['We hypothesized that dietary polyunsaturated fatty acids (PUFA) could affect the expression of serum fatty acid binding protein 5 (FABP5) and CD36 levels and also fatty acid synthase (FAS), and estrogen receptor (ER) expressions in breast cancer cells.', 'A rat mammary cancer model was induced by injection i.p., with 50 mg MNU/kg body weight. Low (13.8% energy) or high-fat (42.5% energy) diets composed mainly of n-6 or n-3 PUFAs originating either from linoleic acid or linolenic acid, respectively, were given for eight weeks. After sacrifice at week 8, serum FABP5 level was examined and immunostainings of CD36, FAS, and ER of breast cancer tissue were observed.', 'By week 8, there was no statistical difference of tumor formation rate between each group. The level of serum FABP5 in the high n-3 group was significantly lower than the low n-6 and high n-6 groups. Immunohistochemistry results showed that there was a significant difference of CD36 expression between the low n-3 group and high n-6 group (p < 0.05). Although the high n-3 group had the most inhibition on FAS and ER expression, there was no statistical difference between each group.'] Do dietary fatty acids affect lipid metabolism and estrogen receptor expression in N-methyl-N-nitrosourea-induced rat mammary cancer model?