Trichomonas vaginalis association with prostate cancer confirmed

The sexually transmitted disease Trichomonas vaginalis was associated with extraprostatic prostate cancer and potentially fatal prostate cancer, according to case-control study results.

Researchers conducted a case-control study nested within the Physicians’ Health Study. All men in the Physicians’ Health Study submitted a blood sample upon enrollment.

In this study, the researchers examined the plasma samples of 673 men diagnosed with prostate cancer up to 18 years after submitting a blood sample and samples from 673 matched healthy participants. The seroprevalence of T. vaginalis was 25% in patients and 21% in control participants.

The researchers said the presence of T. vaginalis was associated with increased risk for diagnosis of advanced-stage prostate cancer (OR=2.17; 95% CI, 1.08-4.37) and increased risk that the cancer would progress to distant metastases or death (OR=2.69; 95% CI, 1.37-5.28).

Thirty-nine men were diagnosed with lethal cancer within five years of blood collection. Between those men and their matched control patients, the 15 men who tested positive for T. vaginalis were more likely to develop lethal disease than the men who tested negative for the STD (OR=6.4; 95% CI, 1.5-27.9).

Despite these positive associations, no statistically significant association was found between the presence of the T. vaginalis infection and total prostate cancer risk (OR=1.23; 95% CI, 0.94-1.61) or high-grade disease (OR for Gleason 7–10 scores=1.10; 95% CI, 0.72-1.68).

In an accompanying editorial, Peter C. Albertsen, MD, with the University of Connecticut Health Center in Farmington, put the results of this study in perspective in an era where diagnosis is dominated by PSA testing.

“Now most men are identified with localized disease usually five to 10 years earlier in the natural course of the disease,” Albertsen wrote. “As a consequence, researchers now have much more difficulty distinguishing clinically significant cancers from indolent disease.

“The outcome of interest, clinically significant prostate cancer, has been contaminated by large numbers of men with indolent disease. Therefore, the sample size needed to identify a statistically significant association with overall prostate cancer risk has increased dramatically,” he wrote. “Failure of the study by Stark et al to find a statistically significant association between T. vaginalis seropositive status and overall prostate cancer risk may therefore be due to a type II error.”

He said that enthusiasm to use PSA testing before “understanding the true clinical impact” may have added addition confounding variables to the diagnosis and treatment of prostate cancer.

Stark JR. J Natl Cancer Inst. 2009;doi:10.1093/jnci/djp306.