The sexually transmitted infection Trichomonas vaginalis may increase the risk of advanced prostate cancer. These results were published in the Journal of the National Cancer Institute.

Trichomonas vaginalis is a single-celled protozoan parasite. It is a common sexually transmitted infection among both men and women. Most men who are infected do not have any symptoms, although some may experience irritation inside the penis or slight discharge. In women, the infection may cause vaginal discharge with a strong odor.

Previous studies have produced mixed results regarding the relationship between Trichomonas vaginalis and risk of prostate cancer. A 2006 report from the Health Professionals Follow-up Study suggested that past infection increased the risk of prostate cancer, but a subsequent report from the Prostate Cancer Prevention Trial did not confirm this finding. To further explore this question, researchers analyzed information from the Physicans’ Health Study.

The current analysis focused on 673 men with prostate cancer and 673 men without prostate cancer. Information about prior Trichomonas vaginalis infection was obtained by testing blood samples for the presence of antibodies to the infection.

• Men with a history of Trichomonas vaginalis infection were 23% more likely to have prostate cancer than men without a history of the infection. This result did not meet the criteria for statistical significance, suggesting that it could have occurred by chance alone.
• Men with a history of Trichomonas vaginalis infection were twice as likely to have prostate cancer that had spread beyond the prostate and were 2.6 times more likely to have prostate cancer that involved the bone or caused death. These results were statistically significant, meaning that they were unlikely to be due to chance.

These results suggest that Trichomonas vaginalis infection may contribute to aggressive prostate cancer. Further research will be necessary, however, to confirm these results.

Reference: Stark JR, Judson G, Alderete JF et al. Prospective study of Trichomonas vaginalis infection and prostate cancer incidence and mortality: Physican’s Health Study. Journal of the National Cancer Institute. 2009;101:1-6.