Background Several inflammation-related factors have been implicated in prostate cancer risk and progression, but the origin of inflammation is unclear. Infections are one possible source, but studies of specific infections have been largely inconclusive. A recent prospective study found that antibody seropositivity against Trichomonas vaginalis was positively associated with subsequent incidence of prostate cancer. This parasitic protozoan has received relatively little attention despite being the most common non-viral sexually transmitted infection. We sought to further explore and extend this hypothesis in an independent population, both for prostate cancer incidence as well as progression.
Methods We conducted a prospective case-control study nested within the Physicians’ Health Study that included 673 prostate cancer cases and 673 individually matched controls. T. vaginalis antibody serostatus was assessed by an ELISA that detects IgG antibodies against purified, recombinant T. vaginalis α-actinin protein. We used conditional logistic regression for analyses of total prostate cancer incidence and Cox proportional hazards models to estimate hazard ratios for lethal prostate cancer (prostate cancer-specific death or development of bony metastases).
Results The seroprevalence of T. vaginalis infection was 21% in controls and 25% in cases. Among cases, the average time between blood draw and prostate cancer diagnosis was 9.3 years (range 0.3 years - 17.9 years). Though not statistically significant, the magnitude of the association between T. vaginalis seropositivity and overall prostate cancer risk (OR: 1.23; 95% CI: 0.94, 1.61) was similar to the original study, which observed a 43% increased risk. Further, seropositive men had a 2.2-fold increase in risk of extraprostatic disease (95% CI: 1.08, 4.37) and a 2.7-fold greater risk of lethal prostate cancer (95% CI: 1.37, 5.28; 39 cases developed bony metastases or died of prostate cancer). Time-to event analyses included 7,776 person-years of follow-up and showed that, compared to seronegative cases, cases with serologic evidence of infection prior to cancer diagnosis had a 50% greater rate of progression to lethal prostate cancer (95% CI: 1.01, 2.16).
Conclusions In this large prospective study, we observed a modest association between anti-T. vaginalis antibodies and overall prostate cancer risk and found that T. vaginalis infection was principally associated with clinically relevant, potentially lethal disease. If our findings are confirmed, T. vaginalis infection may represent a common risk factor for which chemoprevention could reduce burden of aggressive prostate cancer.
Citation Information: Cancer Prev Res 2008;1(7 Suppl):PR-8.
- American Association for Cancer Research