A case-cohort study of diet and risk of benign proliferative epithelial disorders of the breast (Canada).

A case-cohort analysis of the association between diet and risk of benign proliferative epithelial disorders (BPED) of the breast was undertaken within a cohort of 56,537 women who were enrolled in the Canadian National Breast Screening Study (NBSS) and who completed a self-administered dietary questionnaire. (The NBSS is a randomized controlled trial of screening for breast cancer in women aged 40 to 59 years.) BPED are thought to have premalignant potential. Specific hypotheses were that risk of BPED would increase with increasing energy-adjusted fat intake and decrease with increasing energy-adjusted vitamin A and fiber intake. Additionally, we explored the association between calcium intake and risk of BPED. During the active follow-up phase of the NBSS, 657 women in the dietary cohort were diagnosed with biopsy-confirmed incident BPED. For comparative purposes, a subcohort consisting of a random sample of 5,581 women was selected from the full dietary cohort. After exclusions for various reasons, the analyses were based on 545 cases and 4,921 non-cases. Overall, the results were almost uniformly null, and provided little support for the study hypotheses. Rate ratios (95 percent confidence intervals [CI]) for the highest cf the lowest quintile levels for total fat, retinol, beta-carotene, fiber, and calcium were 0.88 (CI = 0.65-1.20), 0.97 (CI = 0.71-1.31), 0.94 (CI = 0.70-1.27), 1.11 (CI = 0.82-1.50), and 0.81 (CI = 0.60-1.07), respectively. There were too few cases of atypical BPED for meaningful analysis, but results for those whose BPED showed no atypia were similar to the overall results. Further analyses conducted separately in the screened and control arms of the NBSS also failed to provide strong support for dietary associations, as did those conducted separately for screen-detected and interval-detected BPED.