Dietary intake of isoflavones and coumestrol and risk of pancreatic cancer in the prostate, lung, colorectal, and ovarian cancer screening trial.

BACKGROUND

Although phytoestrogens modulated pancreatic tumour growth in experimental studies, it remains unclear whether phytoestrogen intake is associated with pancreatic cancer.

METHODS

Of 92,278 persons who completed the Diet History Questionnaire in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, 346 were diagnosed with pancreatic cancer within a median follow-up of 9.4 years. Cox proportional hazards regression was used to evaluate pancreatic cancer risk in relation to phytoestrogen intake.

RESULTS

After adjustment for confounders, intakes of glycitein and formononetin were associated with a reduced risk of pancreatic cancer [highest vs. lowest quartile, hazard ratio (HR) (95% confidence interval (CI)) for glycitein: 0.60 (0.39, 0.92); P for linear trend: 0.01; HR for formononetin: 0.51 (0.37, 0.70); P for linear trend: 0.005]. These associations were stronger and their linear trends across the quartiles of intakes were more statistically significant among ever smokers than never-smokers. A reduced risk was also observed for ever smokers in the highest quartile of total isoflavones or daidzein compared with those in the lowest quartile.

CONCLUSIONS

Our study suggests that high intakes of total isoflavones and some individual isoflavones were inversely associated with pancreatic cancer risk, but this potential protective effect was confined to ever smokers.