Abstract 1884: Dietary intake of phytoestrogens and the risk of prostate cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial
Authors: Reger Michael , Zollinger Terrell , Liu Ziyue , Jones Josette , Zhang Jianjun 
Published: August 2015

Abstract
Prostate cancer is the most common non-cutaneous cancer and second leading cause of cancer death among men in the U.S. Although ecologic and migrant studies suggest that diet plays a role in the etiology of prostate cancer, few specific nutrients that alter its occurrence have been identified in case-control and cohort studies. Phytoestrogens are a family of bioactive compounds that are abundant in soy products and some other food groups (e.g. legumes and chick peas). Experimental studies revealed that phytoestrogen intake may modulate the risk of prostate cancer due to their structural similarity to 17β-estradiol and the resulting competitive binding to estrogen receptors. Despite biological plausibility, it still remains elusive whether phytoestrogen intake influences prostate cancer risk in human populations. Therefore, the objective of the present study was to investigate the associations between dietary intake of phytoestrogens and the risk of total and advanced prostate cancer among 30,097 participants in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO). A total of 3628 cases of prostate cancer (including 396 advanced cases) have been documented during a median follow up of 11.5 years. Advanced prostate cancer were defined as stage II cancer with a Gleason score of ≥8, or stage III or stage IV cancer. Dietary intake of phytoestrogens was assessed with a validated food frequency questionnaire. Cox proportional hazards regression was performed to estimate hazard ratios (HRs) and 95% confidence intervals (CI) for dietary intake of phytoestrogens in relation to prostate cancer risk. After adjustment for confounders, an increased risk of advanced prostate cancer was found for the higher dietary intake of isoflavones (HR: 1.58; 95% CI: 1.11, 2.24), genistein (HR: 1.42; 95% CI: 1.02, 1.98), daidzein (HR: 1.62; 95% CI: 1.13, 2.32), and glycitein (HR: 1.53; 95% CI: 1.09, 2.15). Conversely, it appears that the higher dietary intake of genistein was associated with a reduced risk of non-advanced prostate cancer (HR: 0.88; 95% CI: 0.78, 0.99) and total prostate cancer (HR: 0.90; 95% CI: 0.81, 1.00). The risk estimates presented above were obtained for comparisons between the quintile 5 and quintile 1 of respective phytoestrogen intake. In summary, our analysis of this national prospective cohort study suggests that dietary intake of phytoestrogens modulated the risk of prostate cancer and that some of these effects may differ by the aggressiveness of the disease.
Citation Format: Michael Reger, Terrell Zollinger, Ziyue Liu, Josette Jones, Jianjun Zhang. Dietary intake of phytoestrogens and the risk of prostate cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1884. doi:10.1158/1538-7445.AM2015-1884