We previously observed a positive association between a history of trichomonosis, a sexually transmitted infection caused by the protozoan, Trichomonas vaginalis, and prostate cancer risk in the Health Professionals Follow-up Study. To determine the reproducibility of this finding, we conducted a second, prospective investigation of trichomonosis and prostate cancer in the Prostate Cancer Prevention Trial. Participants were men (>or=55 years of age) with no evidence of prostate cancer at enrollment (n = 18,882). Men were screened annually for prostate cancer, and if not diagnosed during the trial, were offered an end-of-study prostate biopsy. Cases were a sample of men diagnosed with prostate cancer on any biopsy after visit 2 or on their end-of-study biopsy (n = 616). Controls were men not diagnosed with prostate cancer during the trial or on their end-of-study biopsy (n = 616). Controls were frequency-matched to cases by age, treatment arm, and family history of prostate cancer. Serum from visit 2 was tested for anti-T. vaginalis IgG antibodies. No association was observed between T. vaginalis serostatus and prostate cancer. 21.5% of cases and 24.8% of controls had low seropositivity, and 15.2% and 15.0% had high seropositivity. Compared to seronegative men, the odds ratio of prostate cancer for men with low seropositivity was 0.83 [95% confidence interval (CI): 0.63-1.09), and that for men with high seropositivity was 0.97 (95% CI: 0.70-1.34). Given the original strong biologic rationale and potential for prevention, additional studies are warranted to help resolve discrepancies between study findings and to further investigate this hypothesis from a variety of different approaches.
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