Men in the study who had been infected with the STD trichomoniasis were only slightly more likely to develop prostate cancer years later, compared to men with no documented evidence of prior infection.
But they were nearly three times as likely to die of the disease once they had prostate cancer, epidemiologist and study co-author Lorelei A. Mucci, ScD, tells WebMD.
"Our finding suggests that infection may make prostate cancers more aggressive and more likely to progress," she says.
STD and Prostate Cancer
Trichomoniasis affects both men and women and as many as 7.4 million new infections occur each year, according to the CDC.
The STD is caused by the parasite Trichomonas vaginalis.
Though easily treated with medication, 50%-75% of men with trichomoniasis never develop symptoms so they never find out they have the STD. And many, but not all, clear the infection in a matter of weeks without treatment. Also, people can be reinfected even after treatment.
At least one previous study has suggested a link between trichomoniasis and more aggressive prostate cancers, but that study was smaller and had shorter follow-up than the one reported by Mucci and colleagues in the Sept. 9 online version of the Journal of the National Cancer Institute.
Using data from an ongoing trial involving more than 22,000 male physicians first recruited in 1982, the researchers compared prostate cancer incidence and outcomes among men with and without evidence of infection with the STD.
A history of trichomoniasis infection was confirmed by testing stored blood samples drawn from the men soon after they entered the study.
The samples revealed a slight, but not statistically significant, increase in prostate cancers among men with evidence of a prior infection.
But men who had evidence of prior infection of the STD when they entered the study were far more likely to develop aggressive prostate cancers and they were more likely to die of their cancer.
Detecting Aggressive Prostate Cancer
Infection leads to inflammation, and inflammation has long been suspected of playing a leading role in the development and progression of prostate cancer.
Although previous studies examining other STDs have largely failed to show an association with prostate cancer, most did not have the long follow-up that the newly reported study did, American Cancer Society director of prostate cancer Durado Brooks, MD, MPH, tells WebMD.
"We can say from this study that there may be a link between this sexually transmitted infection and more aggressive prostate cancer, but more research is needed to confirm this," he says.
If the link is confirmed, the finding could offer much needed insight into which prostate cancers will become deadly and which will not, he says.
The introduction of prostate-specific antigen (PSA) testing in the late 1980s led to a doubling in the number of prostate cancers diagnosed annually.
It has become clear in recent years that many of the cancers found with PSA testing are not likely to progress, but determining which patients need aggressive treatment and which do not remains a problem.
"We need more markers to tell us at the time of diagnosis how aggressive a cancer will be," Brooks says.