Associations between Diet Quality Scores and Risk of Postmenopausal Estrogen Receptor-Negative Breast Cancer: A Systematic Review

Background: Estrogen receptor-negative (ER-) breast cancer tends to have poorer prognosis than estrogen receptor-positive breast cancer. A number of studies have examined the association between diet quality as measured by various diet quality scores and the risk of ER-breast cancer. Objective: This systematic review aimed to summarize existing evidence on this topic. Methods: Medline and Embase searches were conducted until 2 April 2017 for cohort and case-control studies on diet quality scores and ER-breast cancer. Results: We included 6 prospective cohort studies and 1 case-control study on postmenopausal ER-breast cancer: 4 from Europe and 3 from the United States. There were 12 different diet quality scores: 2 versions of the Dietary Inflammatory Index, 4 versions of the Mediterranean diet score, the Healthy Eating Index, the Alternate Healthy Eating Index, the Dietary Approaches to Stop Hypertension (DASH) score, and 3 versions of low-carbohydrate diet scores that differentiate between different sources of protein and fat. Of the 4 studies on Mediterranean diet scores, 3 showed a significant inverse association with postmenopausal ER-breast cancer, whereas no consistent association was observed with the other diet quality scores. Although most diet quality scores in this review share similar food components, most of the non-Mediterranean diet scores were represented by only 1 study each, and the associations with postmenopausal ER-breast cancer were mixed. All studies were adjusted for multiple covariates. Conclusion: This systematic review shows mixed results for an association between a variety of diet quality scores and postmenopausal ER-cancer. However, results from different versions of the Mediterranean diet scores are more consistent and suggest an inverse relation with ER-breast cancer.