Local response to Trichomonas vaginalis in the prostate may have a role in the development of advanced prostate cancer and for clinically relevant, potentially life-threatening prostate cancer, data suggest.

Researchers conducted a case-control study nested within the Physicians’ Health Study that included 673 men with prostate cancer (cases) and 673 individually matched control subjects without prostate cancer. Using blood samples collected at baseline in 1982, the investigators tested for antibodies against T. vaginalis.

Case subjects were aged 68.7 years on average at the time of prostate cancer diagnosis.  Approximately 54% of cases had Gleason scores of 2-6 and 83% had stage T1 or T2 disease. The mean time between blood collection and prostate cancer diagnosis was 9.3 years (range 0.3 – 17.9 years). The seroprevalence of T. vaginalis was 25% in cases and 21% in controls.

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Overall, T. vaginalis seropositivity was not significantly associated with total prostate cancer risk or high-grade disease, but it was associated with a significant twofold increased risk of advanced prostate cancer, and an almost three-fold increased risk of prostate cancer that progresses to bone metastases and death, according to a report in the Journal of the National Cancer Institute (2009; published online ahead or print). This increased risk was independent of BMI, smoking status, aspirin use, age at diagnosis, and follow-up time.

A previous study found an association between risk of prostate cancer and  T. vaginalis seropositivity, but it was not large enough to determine if there was a link between the infection and advanced and lethal disease. It is believed that inflammation resulting from T. vaginalis infection may be involved in the pathogenesis of these cancers.  T. vaginalis infects an estimated 174 million people globally each year and is the most common non-viral sexually transmitted infection. It can infect the prostate without producing symptoms in most men.

While more research is needed to confirm these findings, the data do suggest that certain infections may be causing inflammation and that there may be anti-inflammatory agents that could ameliorate the inflammation.  Moreover, since T vaginalis infection is easily treatable with an inexpensive antibiotic regimen, the results from this study suggest that prevention or early treatment of T vaginalis infection could be a target for prostate cancer prevention.

“Prostate cancer is the most common cancer among men in western countries, and the second leading cause of cancer-specific mortality. Identifying modifiable risk factors for the lethal form of prostate cancer offers the greatest opportunity to reduce suffering from this disease,” said first author Jennifer Stark, ScD, a post-doctoral fellow at the Harvard School of Public Health (HSPH) in Boston.

“Our findings are good news because these types of infections are easy to diagnose and easy to treat,” said senior author Lorelei Mucci, ScD, Assistant Professor of Epidemiology at the HSPH. “We think inflammation is a key factor particularly in aggressive prostate cancer and so it may be possible to lower risk of clinically significant disease through several different avenues.  Additional research will need to focus on what agents out there may help with chronic inflammation.”

She said that there may be additional sexually transmitted diseases that are also important risk factors for aggressive and lethal prostate cancer.

For example, Dr. Mucci said there has also been “a hint in the literature” that Chlamydia trachomatis may be associated with aggressive forms of prostate cancer, although more research is needed.  Moreover, about three years ago, researchers identified a new virus, xenotropic murine leukemia virus-related virus, which may prove to be important for prostate cancer.