Adherence to the Western, Prudent and Mediterranean dietary patterns and breast cancer risk: MCC-Spain study

Objective: To externally validate the previously identified effect on breast cancer risk of the Western, Prudent and Mediterranean dietary patterns. Study design: MCC-Spain is a multicase-control study that collected epidemiological information on 1181 incident cases of female breast cancer and 1682 healthy controls from 10 Spanish provinces. Three dietary patterns derived in another Spanish case-control study were analysed in the MCC-Spain study. These patterns were termed Western (high intakes of fatty and sugary products and red and processed meat), Prudent (high intakes of low-fat dairy products, vegetables, fruits, whole grains and juices) and Mediterranean (high intake of fish, vegetables, legumes, boiled potatoes, fruits, olives, and vegetable oil, and a low intake of juices). Their association with breast cancer was assessed using logistic regression models with random province-specific intercepts considering an interaction with menopausal status. Risk according to tumour subtypes based on oestrogen (ER), progesterone (PR) and human epidermal growth factor 2 (HER2) receptors (ER +/PR + HER2; HER2+; ER- /PR- & HER2-) -was evaluated with multinomial regression models. Main outcome measures: Breast cancer and histological subtype. Results: Our results confirm most of the associations found in the previous case-control study. A high adherence to the Western dietary pattern seems to increase breast cancer risk in both premenopausal women (OR4th vs 1st quartile (95% CI):1.68 (1.02;2.79); ORISD-increase (95% CI):1.19 (1.02;1.40)) and postmenopausal women (OR4th vs 1st quartile(95% CI):1.48(1.07;2.05); ORISD-increase(95% CO: 1.14 (1.01;1.29)). While high adherence to the Prudent pattern did not show any effect on breast cancer, the Mediterranean dietary pattern seemed to be protective, but only among postmenopausal women (OR4th vs 1st quartile (95% CI): 0.72 (95% CI 0.53;0.98); p-int = 0.075). There were no significant differences by tumour subtype. Conclusion: Dietary recommendations based on a departure from the Western dietary pattern in favour of the Mediterranean diet could reduce breast cancer risk in the general population.