Experiments were performed to investigate whether the type of
dietary fat might affect
metastasis from the 13,762 mammary
tumor. Female Fischer 344 retired breeder rats were placed into one of five dietary groups: 23% (wt/wt) and 5% (wt/wt)
corn oil (HFCO, LFCO), 20% (wt/wt) and 5% (wt/wt)
olive oil (HFOO and LFOO), or 20% (wt/wt)
beef tallow (HFBT). After four weeks on the diets, each rat had a 2-mm3 piece of the
tumor subcutaneously implanted. Primary
tumor growth and
body weight were monitored weekly for 40 days. At necropsy, the average volume of pulmonary
metastases in the HFCO animals (
n = 30) was significantly greater than in the other four groups. Among the four groups that did not differ significantly from each other, the rank order in average volume of pulmonary
metastasis was as follows: HFOO (n = 25), HFBT (n = 26), LFOO (n = 25), and LFCO (n = 18). Growth of the primary
tumor did not vary appreciably among the five groups despite the significant difference in pulmonary
metastasis volume. The diets varied considerably in
fatty acid content; the most salient difference was that the HFCO diet, which stimulated
metastasis significantly more than the other diets did, contained about four times more
linoleic acid (18:2) than the other diets. The relevance of this difference and other
fatty acid differences is discussed. These results suggest that the quality of
dietary fat can be an important determinant of pulmonary
metastasis from the 13,762 mammary
tumor in retired breeder rats.