Though testicular cancer remains relatively uncommon, rates
of the disease have risen in many countries since the 1970s,
a new study shows.
Testicular cancer is known to be most common among white
men, and worldwide, rates of the disease are still highest
in the U.S., Canada, Australia and Europe -- particularly
in Nordic countries such as Denmark and Norway.
But researchers at National Cancer
Institute in Bethesda, Maryland, have found that
rates of the disease rose between 1973 and 1997 in many
parts of the world -- including traditionally low-incidence
countries.
It's "implausible," the researchers report in the International
Journal of Cancer, that better diagnosis of the disease
explains the rise, since there is no widespread screening
for the cancer and most men are still diagnosed only after
symptoms arise.
Instead, Dr. Mark P. Purdue and his colleagues speculate,
changes over time in certain risk factors for testicular
cancer may be at work. What those factors are, however,
is unclear, according to the researchers.
Testicular cancer, which usually arises in young men, remains
a relatively rare disease, even in countries considered
high-incidence. In the U.S., the disease accounts for about
1 percent of all cancers diagnosed in men.
Researchers have identified certain risk factors for the
disease -- such as white race, family history of testicular
cancer, or being born with an undescended testicle or certain
other congenital abnormalities.
But the role of factors related to lifestyle and environment
has been hard to pin down.
According to Purdue's team, some studies have suggested
that men whose mothers gave birth to them at an older age
have an elevated risk of testicular cancer, possibly due
to elevated levels of maternal estrogen during pregnancy.
Other theorized risk factors include low birthweight, younger
age at puberty and certain viral infections in childhood.
None of these, however, have been conclusively tied to testicular
cancer.
More research into how suspected risk factors have changed
over time in different populations "may yield important
insight into the causes of the widespread increase in testis
cancer risk," Purdue and his colleagues write.
Their study is based on 25 years' worth of data from international
cancer registries. Overall, rates of testicular cancer between
1973 and 1997 were highest in Denmark and lowest in Zimbabwe.
But over time, rates of testicular cancer rose in every
population studied -- by 60 percent, on average -- though
the increases were strongest mainly in the regions that
have traditionally had the highest incidence. In the U.S.,
the incidence among white men climbed 47 percent, compared
with 23 percent among black men.
And in Nordic countries, cancer rates rose anywhere from
59 percent to 86 percent.
One standout was Puerto Rico, a low-incidence region that
nonetheless had the biggest jump in the rate of testicular
cancer, at 220 percent. This, however, is a reflection of
the "extremely low" incidence seen in Puerto Rico in the
1970s, the researchers note.
On the brighter side, there were some signs that in the
1990s, the rise in testicular cancer was leveling off in
the U.S. and certain other regions. Further research of
more recent data, according to Purdue's team, should help
show whether rates are indeed stabilizing.
SOURCE: International Journal of Cancer, July 10, 2005.
