Background and purpose: Despite studying the relationship between breast cancer and dietary factors in previous studies, ignoring the cancer phenotype can affect the association between diet and breast cancer. The aim of this study was to determine the association between dietary patterns and HER2 among Iranian women. 

Materials and methods: In a case-control study, 150 new cases with ductal or lobular in situ or invasive breast cancer and without a previous history of the disease were selected. Also, 150 age-matched controls were included in the study. Data including demographic characteristics, food frequency, and physical activity were recorded using relevant questionnaires. Also, the information regarding HER-2 factor was obtained from patients records. Factor analysis was used to identify major dietary patterns. The association between these patterns and breast cancer was examined by logistic regression analysis.

Results: Two major dietary patterns were identified. After adjusting for potential confounders, participants who had higher scores for unhealthy dietary patterns (mayonnaise, French fries, soft drinks, pickles, red or processed meat, potatoes, sweets and desserts) and healthy dietary patterns (fruits and fruit juices, vegetables, low-fat dairy products, spices, nuts, fish, egg, legumes and low intake of  hydrogenated fats) were more (OR: 4.12, 95%CI: 2.31-7.3) and less (OR: 0.17, 95% CI: 0.30-0.95)  prone to develop breast cancer, respectively. A healthy dietary pattern reduced the risk of HER-2 positive breast cancer (OR: 0.11, 95% CI: 0.04-0.25).

Conclusion: Healthy dietary pattern reduced the overall risk of breast cancer and was inversely associated with HER-2 positive tumors, indicating a poor prognosis of the disease.