WCRF/AICR recommendation adherence and breast cancer incidence among postmenopausal women with and without non-modifiable risk factors

Taller height, family history of breast cancer, greater number of years of potential fertility and nulliparity are established non-modifiable risk factors for postmenopausal breast cancer. Greater adherence to the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) diet, physical activity and body weight recommendations has previously been shown to be associated with lower breast cancer risk. However, no prior studies have evaluated whether women with non-modifiable risk factors receive similar benefits from recommendation adherence compared to women without these risk factors. In the Iowa Women's Health Study prospective cohort, we investigated whether associations of WCRF/AICR recommendation adherence differed by the presence/absence of non-modifiable breast cancer risk factors. Baseline (1986) questionnaire data from 36,626 postmenopausal women were used to create adherence scores for the WCRF/AICR recommendations (maximum score = 8.0). Overall and single recommendation adherence in relation to breast cancer risk (n = 3,189 cases) across levels of non-modifiable risk factors were evaluated using proportional hazards regression. Mean adherence score was 5.0 points (range: 0.5-8.0). Higher adherence scores (score ≥6.0 vs. ≤3.5, HR = 0.76, 95% CI = 0.67-0.87), and adherence to the individual recommendations for body weight and alcohol intake were associated with a lower breast cancer incidence. While not statistically significant among women with more non-modifiable risk factors (score ≥6.0 vs. ≤3.5, HR = 0.76, 95% CI = 0.36-1.63), hazard ratios were comparable to women with the no non-modifiable risk factors (score ≥6.0 vs. ≤3.5, HR = 0.74, 95% CI = 0.49-0.93) (p-interaction = 0.57). WCRF/AICR recommendation adherence is associated with lower breast cancer risk, regardless of non-modifiable risk factor status.