Increasing evidence — much of it discovered and
actively being explored by Hopkins scientists — suggests that chronic
inflammation may be an important instigator of prostate cancer.
One source of chronic inflammation in the prostate is sexually transmitted
infections (STIs, more commonly known as STDs).
Could having a sexually
infection make a man more
susceptible to prostate cancer?
And this begs the question — at least to epidemiologist
Elizabeth A. Platz, Sc.D., one of the pioneers in this area of research,
and colleagues including Jonathan M. Zenilman, M.D., Angelo M. De
Marzo, M.D., Ph.D., and postdoctoral fellow Siobhan Sutcliffe, Ph.D:
Could having a sexually transmitted infection make a man more susceptible
to developing prostate cancer?
Before the scientists could answer this question,
they had to narrow down the playing field. Which, of the more than
30 known sexually transmitted infections, should they study? First,
they looked for an infection known to cause extensive inflammation
in the prostate. They also looked for a silent one—one that causes
no symptoms, that stays below the radar, in effect. A quiet infection,
they reasoned, "would be less likely to be treated and cured, and
thus might persist in the man's genitourinary tract." One infection
that fit both criteria was trichomonosis, a sexually transmitted
infection caused by the protozoan, Trichomonas vaginalis. "About
20 years ago, a pathologist named William A. Gardner Jr. noted that
T. vaginalis was capable of infecting the prostate and
causing a strong inflammatory immune response," explains Platz.
"And yet, despite this interesting finding, essentially no work
was done on the possible role that T. vaginalis might play
in the development of prostate cancer."
To investigate this, the scientists selected 691
men with prostate cancer and 691 men without prostate cancer from
participants in a large, Harvard-based project called the Health
Professionals Follow-up Study. The lead role in the investigation
was taken by Sutcliffe. Working with microbiologist John F. Alderete,
Ph.D., who developed an assay to detect antibodies against T. vaginalis
and tested the men's samples, they found that about 11 percent of
men had antibodies against T. vaginalis. And significantly,
"men who had these antibodies were about 40 percent more likely
to develop prostate cancer than men who did not have these antibodies,"
Even more exciting — in research that continues
work by Platz and others investigating the use of nonsteroidal anti-inflammatory
agents as a preventive measure against prostate cancer— "We then
separated men into those who did and did not regularly use aspirin,"
Platz says. Aspirin reduces inflammation. And in this study, among
men who regularly used aspirin, those who had antibodies against
this infection had the same risk of prostate cancer as men who had
not been exposed to it. "But, among men who did not regularly use
aspirin, those who had antibodies against T. vaginalis
were twice as likely to develop prostate cancer." Sutcliffe, Platz
and colleagues are quick to point out that these results are preliminary,
and that much further study is needed. Even so, the Hopkins researchers
are excited by these findings and now are looking to see whether
young men in the U.S. military with antibodies against T. vaginalis
have higher blood levels of a marker of prostate inflammation and
cell damage than those who don't have antibodies. "This may indicate
that T. vaginalis infected the prostate and caused cell
damage in these men,” says Platz.