Plant foods and oestrogen receptor α- and β-defined breast cancer: observations from the Malmo Diet and Cancer cohort

The associations between plant foods and breast cancer incidence are inconsistent. The objective of this study was to examine prospectively the association between dietary fibre, plant foods and breast cancer, especially the association between plant food intake and oestrogen receptor (ER) alpha- and beta-defined breast cancer. Among women without prevalent cancer from the population-based prospective Malmo Diet and Cancer cohort (n = 15 773, 46-75 years at baseline), 544 women were diagnosed with incident invasive breast cancer during a mean follow-up of 10.3 years. Information on dietary habits was collected by a modified diet history method. ER status of the tumours was determined by immunohistochemistry using tissue microarray. Cox proportional hazards regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs) of breast cancer associated with fibre and 11 plant food groups. High-fibre bread was significantly associated with a decreased breast cancer incidence (HR, 0.75; 95% CI, 0.57-0.98, for highest compared with lowest quintile). The other plant food groups were not significantly associated with breast cancer incidence. There was a tendency for a negative association for high-fibre bread among ER alpha (+) breast cancer (P for trend = 0.06) and ER beta (+) breast cancer (P for trend = 0.06). Fried potatoes were statistically significantly associated with increased risk of ER beta (-) breast cancer (P = 0.01). This study suggests that different plant foods may be differently associated with breast cancer, with fibre-rich bread showing an inverse association. We did not observe strong evidence for differences in incidence according to the ER alpha and ER beta status of breast cancer.