Intake of flavonoids is associated with the incidence of breast cancer, but the association between the intake of flavonoids and cancer recurrence is unclear. This study aimed to investigate the hypothesis that intake of flavonoids and flavonoid-rich foods is negatively associated with cancer recurrence. Among 572 women who underwent breast cancer surgery, 66 patients had a cancer recurrence. Dietary data were collected using a structured 24-h dietary recall, and intake of flavonoids was calculated based on the Korea Rural Development Administration flavonoid database. Among overweight and obese patients, disease-free survival was associated with intake of flavonoids (p = 0.004) and flavonoid-rich foods (p = 0.003). Intake of flavonoids (hazard ratio (HR) = 0.249, 95% confidence interval (CI): 0.09–0.64) and flavonoid-rich foods (HR = 0.244, 95% CI: 0.09–0.66) was negatively associated with cancer recurrence after adjusting for confounding factors in overweight and obese patients. Consumption of flavonoids and flavonoid-rich foods was lower in overweight and obese patients with cancer recurrence than those without recurrence and in normal-weight patients. This study suggests that intake of flavonoids and flavonoid-rich foods could have beneficial effects on cancer recurrence in overweight and obese breast cancer survivors.

Objectives Flavonoid intakes have been shown to associate with breast cancer incidence, but it is not clear the association between flavonoids and cancer recurrence. The purpose of the present study was to investigate the hypothesis that intakes of flavonoids and flavonoid-rich foods were negatively associated with cancer recurrence. Methods Among 572 women after breast cancer surgery, 66 patients had cancer recurrence during follow–up until 114 months with a median period of disease-free survival of 43 months ranged 6–103 months. Dietary data were collected using structured 24-h dietary recall, and the intake of flavonoid was calculated based on the Korea Rural Development Administration flavonoid database. Results There was no significant association of flavonoid and flavonoid-rich food intake with cancer recurrence and disease-free survival among all patients. On the other hand, among overweight and obese patients, Kaplan-Meier survival curves revealed a significant effect of dietary flavonoids (P = 0.04) and flavonoid-rich foods (P = 0.03) on disease-free survival, but not overall survival. Intakes of flavonoid (HR = 0.244, 95% CI: 0.09–0.66) and flavonoid-rich food (HR = 0.223, 95% CI: 0.08–0.59) were also negatively associated with cancer recurrence after adjusting for confounding factors in overweight and obese patients. Consumption of flavonoids and flavonoid-rich foods was lower in overweight and obese patients with cancer recurrence than those without recurrence. Conclusions To the best of our knowledge, this was the first study to examine the association between flavonoid intake and cancer recurrence/disease-free survival in breast cancer patients. The present study suggested that intakes of flavonoids and flavonoid-rich foods could have a beneficial effect on cancer recurrence among overweight and obese breast cancer survivors. Further clinical studies are needs to confirm whether supplementation of flavonoids reduces cancer recurrence. Funding Sources This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2018R1A2B6002486).