Effect of dietary stearic acid on the genesis of spontaneous mammary adenocarcinomas in strain A/ST mice.

Strain A/ST female mice maintained on a high fat (15%) diet in which stearic acid was the major lipid component developed initial spontaneous mammary adenocarcinomas at an older age than mice fed a low fat (4.5%) stock diet. Mice placed on the SA diet at weaning developed tumors at 15.7 +/- 0.87 months compared to 12.7 +/- 0.43 months for those retained on the stock diet (p less than .05). Placing mice on the SA diet at 11.5 months resulted in a smaller but significant increase in the latency period (5.0 +/- 0.86 vs 3.0 +/- 0.57 months +/- 0.57 mo), (p less than .05). Fatty acid analyses of non-tumorous mammary tissue from mid-pregnant mice and of tumor tissues showed that feeding large amounts of 18:0 did not result in increases in the proportion of 18:0. Significant reductions in the percentages of polyunsaturated fatty acids (PUFA) was found in tissues on mice fed the SA diet. The percentage of 18:2 was reduced in both types of tissues; 20:3 and 20:4 was reduced in tumor tissues. Distribution of C18 fatty acids in plasma membranes of tumors of mice fed the two diets were similar; percentages 18:2 was higher in plasma membranes of non-tumorous tissues of mice fed the SA diet. These results suggest that dietary stearic acid interferes with the availability of certain PUFA required for tumor production.