A dietary pattern resulting in higher circulating estrogen levels is associated with an increased risk of postmenopausal estrogen receptor (ER)-positive breast cancer, according to a prospective study published in the International Journal of Cancer.1

Serum and urinary levels of estrogen are correlated with an increased risk for postmenopausal breast cancer, and diet has been extensively studied as a potential modifiable risk factor.

The present study used a statistical approach called reduced rank regression (RRR), in which biomarkers can be used to develop a dietary pattern that can be evaluated against disease endpoints. Several previous studies that used RRR to evaluate the effect of an estrogen-related dietary pattern (ERDP) on the risk of breast cancer had mixed results — an analysis of the Nurses’ Health Study showed no effect, whereas a Swedish cohort demonstrated a positive association.

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This study analyzed baseline serum samples and food questionnaire data from a subset of women that included 260 cases and 393 controls from the prospective cohort study — the Prostate, Lung, Colorectal & Ovarian Cancer Screening Trial (PLCO) — to determine which food groups were associated with serum levels of unconjugated estradiol (E2) and the 2/16 ratio. RRR modeling was then used to determine the ERDP, which included foods such as cheese, processed meats, refined grains, cruciferous vegetables, tomatoes, and fish/shellfish high in omega-3 fatty acids.

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According to Mark Guinter, PhD, MPH, of the American Cancer Society (ACS) in Atlanta, Georgia, and lead author of the study, “using statistics, we were able to determine which food groups were most strongly related to the estrogen levels, and due to the strength of that relationship, those food groups were identified as contributors to the ERDP.” He told Cancer Therapy Advisor that, for example, high cheese intake was common among women with high serum estrogen levels, whereas high coffee intake was common among women with low circulating estrogen.

“In this type of analysis, the food groups included are completely dependent upon the dietary responses and estrogen levels of the given study population that was used,” Dr Guinter said. He cautioned that “if this same approach was used in a different study population, the food groups included might be different, although we hope to see a lot of overlap.”

These data were then applied to a larger cohort that included 27,488 women from the intervention arm of the PLCO study to evaluate the association with breast cancer development during the follow-up period. In the study, 4.9% of the total variation in estrogen metabolites was attributed to ERDP.