| Sumario: | We investigated how timing influences the role of diet in breast cancer risk with a cross-sectional study of pre-malignant change in breast tissue. Women with an elevated risk of developing breast cancer (33 premenopausal and 32 postmenopausal) completed the National Cancer Institute's food frequency questionnaire and underwent random periareolar fine-needle aspiration for evaluation of cytologic atypia, an established risk biomarker. Fatty acid composition of breast adipose was measured in 32 (49%) subjects. We found that premenopausal and postmenopausal women had similar diets, but the associations between atypia and intake of total n-3 polyunsaturated fatty acids (PUFA) and soy differed by menopause status (bothPinteraction< 0.001). Total n-3 PUFA intake was inversely associated with atypia among premenopausal women (P< 0.0001), but not among postmenopausal women (P= 0.91); associations were similar for soy (P= 0.0003 andP= 0.48, respectively). This pattern of dietary interaction with menopause was mirrored in tissue fatty acids (Pinteraction< 0.05), wherein 1) higher levels of linolelaidic acid (an industrially-produced trans fat) and 2) lower levels of docosahexaenoic acid (the predominant long-chain n-3 PUFA) in breast adipose were associated with atypia in premenopausal (bothP< 0.05) but not postmenopausal women (bothP> 0.37). Dietary associations with breast cancer risk are stronger prior to menopause.
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