A, L Richiardi, O Akre, SM Montgomery and P Sparén. 2003.
Age at Immigration and Duration of Stay in Relation to Risk
for Testicular Cancer Among Finnish Immigrants in Sweden.
of the National Cancer Institute 95:1238–40.
cancer is increasingly common in a number of countries, including
in North America and Europe. Some countries have markedly higher
rates. For example, testicular cancer is more than twice as high
in Sweden as it is in Finland, and twice as high in Denmark as it
is in Sweden.
this new study, examining the incidence of testicular cancer in
men who have immigrated from Finnish to Sweden, Ekbom and his colleagues
provide strong evidence that environmental exposures early in life
are likely to be major determinants for this disease. Their findings
are consistent with Skakkebæk's theory that the origins of
testicular cancer and several other testicular maladies are part
of single syndrome, testicular
dysgenesis syndrome, whose origins lie in disruption of the
development of the fetal testis.
did they do? Ekbom et al. compared the incidence
of testicular cancer in Finnish immigrants to Sweden with the incidence
rates of the general Swedish population. In particular, they were
interested in whether men moving to Sweden became at risk to testicular
cancer at rates comparable to Swedish men, or whether they more
closely resembled men in their native Finland.
obtained data from the national health registry of Swedish residents,
which includes information not only about health status but also,
for immigrants, about year and origin of immigration. Using these
data, they determined the incidence of testicular cancer in the
immigrants, and compared them to data from the general Swedish population.
did they find? The cohort studied included 93,172 men who
had immigrated from Finland to Sweden from 1969 to 1994. Finnish
immigrants in Sweden had fewer than half the number that would have
been expected based on testicular cancer rates in Sweden. The ratio
of observed cases to expected cases
was 0.34 (95% confidence interval 0.21-0.53). The incidence in the
immigrants did not differ from the incidence rates in Finnish men
who had not emigrated to Sweden. Neither age at immigration nor
duration of stay affected the results.
does it mean? The authors interpret their results to implicate
a combination of genetic and environmental factors. Genetic differences
may contribute to the overall difference between Finland and Sweden,
but they cannot explain the increasing incidence of testicular cancer,
nor differences between Finnish and Estonian men or Swedish and
Danish men (who are more similar to one another genetically than
Finnish men are to Swedish men).
fact that neither age at immigration nor duration of stay altered
the results strongly implicates events very early in life. The authors
observe: "Thus, it is likely that differences between the populations
with respect to exposure of environmental factors early in life
explain the low incidence of testicular cancer among Finnish immigrants.
It is highly plausible that susceptibility to these exposures occurs
in utero when the testicles are developing and differentiating
in the presence of numerous growth-regulating factors."
Ekbom et al.'s results strongly implicate environmental
exposures early in life, they do not identify what exposures might
be responsible. They comment that because the risk of testicular
cancer is largely determined in utero, the differences
observed today between incidence rates in Sweden vs. Finland "would
be attributable to environmental differences that were present approximately
30 years ago."
results are consistent with a recent
study finding that testicular cancer risk is more tightly associated
with organochlorine levels in a mother's serum than a son's, both
measured at the time of diagnosis of testicular cancer in the son.