Background: The association between red meat intake and breast cancer is unclear, but most studies have assessed diet in midlife or later. Although breast tumors differ clinically and biologically by hormone receptor status, few epidemiologic studies of diet have made this distinction.
Methods: Red meat intake and breast cancer risk were assessed among premenopausal women aged 26 to 46 years in the Nurses' Health Study II. Red meat intake was assessed with a food frequency questionnaire administered in 1991, 1995, and 1999, with respondents followed up through 2003. Breast cancers were self-reported and confirmed by review of pathologic reports.
Results: During 12 years of follow-up of 90,659 premenopausal women, we documented 1021 cases of invasive breast carcinoma. Greater red meat intake was strongly related to elevated risk of breast cancers that were estrogen and progesterone receptor positive (ER+/PR+; n = 512) but not to those that were estrogen and progesterone receptor negative (ER-/PR-; n = 167). Compared with those eating 3 or fewer servings per week of red meat, the multivariate relative risks (95% confidence intervals) for ER+/PR+ breast cancer with increasing servings of red meat intake were 1.14 (0.90-1.45) for more than 3 to 5 or fewer servings per week, 1.42 (1.06-1.90) for more than 5 per week to 1 or fewer servings per day, 1.20 (0.89-1.63) for more than 1 to 1.5 or fewer servings per day, and 1.97 (1.35-2.88) for more than 1.5 servings per day (test for trend, P = .001). The corresponding relative risks for ER-/PR- breast cancer were 1.34 (0.89-2.00), 1.21 (0.73-2.00), 0.69 (0.39-1.23), and 0.89 (0.43-1.84) (test for trend, P = .28). Higher intakes of several individual red meat items were also strongly related to elevated risk of ER+/PR+ breast cancer.
Conclusion: Higher red meat intake may be a risk factor for ER+/PR+ breast cancer among premenopausal women.