Polyunsaturated fatty acids in serum phospholipids and risk of breast cancer: a case-control study from the Janus serum bank in Norway.

We have tested the hypothesis that specific polyunsaturated fatty acids (PUFA) of the n-3 and n-6 families, as measured in serum phospholipids, are negatively associated with the risk of breast cancer. The study is based on serum samples from women who have donated blood to the Janus serum bank at the University Hospital in Oslo, Norway. It consists of sera from 87 women who developed breast cancer (cases) subsequent to blood donation and 235 women who were free of any diagnosed cancer (controls), but were of similar age and had similar blood storage time as the cases. We measured fatty acids (monounsaturated, polyunsaturated and saturated) in serum phospholipids, and made comparisons between cases and controls. The results showed that there was an inverse relation between the n-6 PUFA linoleic acid (18:2n-6) and risk of breast cancer, but this association was restricted to women who were 55 years and younger. In this age group, the relative risk (odds ratio) of women in the highest quartile of linoleic acid was 0.4 (95% confidence limits, 0.2 and 1.0) compared with women in the lowest quartile, and there was a negative trend over quartiles of linoleic acid (Mantel's chi for trend = -2.49, P < 0.02). No association was noted between the n-3 PUFA of marine oil origin and breast cancer risk. If the measured concentration of linoleic acid in serum phospholipids reliably reflects dietary intake, these data suggest that linoleic acid in the diet may decrease breast cancer risk among women at premenopausal and perimenopausal age. No similar association with n-3 unsaturated fatty acids was observed. It is noteworthy that none of the measured fatty acids (saturated or unsaturated) showed a positive association with breast cancer risk.