• Department of Obstetrics and Gynecology, the First Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, Zhejiang, China.
• Department of Epidemiology and Health Statistics, School of Public Health and Management, Wenzhou Medical University, Wenzhou, Zhejiang, China.

Estrogen plays crucial roles in ovarian tumorigenesis. Phytoestrogens (PEs) are a type of daily dietary nutrients for humans and possess a mild estrogenic characteristic. This study aimed to assess the correlation of the consumption of dietary PEs with ovarian cancer risk using data in the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Participants were enrolled in PLCO from 1993 to 2001. Hazard ratios (HRs) and 95% confidence intervals (CIs) were utilized to determine the association between the intake of PEs and ovarian cancer occurrence, which were calculated by the Cox proportional hazards regression analysis. Totally, 24,875 participants were identified upon completion of the initial dietary questionnaire (DQX). Furthermore, the analysis also included a total of 45,472 women who filled out the diet history questionnaire (DHQ). Overall, after adjustment for confounders, the dietary intake of total PEs was significantly associated with the risk of ovarian cancer in the DHQ group (HRQ4vsQ1 = 0.69, 95% CI: 0.50-0.95; P for trend = 0.066). Especially, individuals who consumed the highest quartile of isoflavones were found to have a decreased risk of ovarian cancer in the DHQ group (HRQ4vsQ1 = 0.68, 95% CI: 0.50-0.94; P for trend = 0.032). However, no such significant associations were observed for the DQX group. In summary, this study suggests that increased dietary intake of total PEs especially isoflavones was linked with a lower risk for developing ovarian cancer. More researches are necessary to validate the findings and explore the potential mechanisms.