Ethnic and socioeconomic trends in
testicular cancer incidence in New Zealand
Diana Sarfati, Caroline Shaw, June Atkinson, James Stanley, Tony Blakely.
University of Otago Wellington, New Zealand
Background
Results
 Testicular cancer is the most common cancer
diagnosed among young men.
 Testicular cancer (TC) is increasing rapidly in
developed countries, but drivers of these trends
remain obscure.
Discussion
 Rates of testicular cancer vary markedly
 In total there were 2,028 cases of testicular
cancer registered among men aged 15-44 years
between 1981 and 2004.
 Ethnic differences in TC incidence within and
between countries are often marked.
 White populations consistently have the
highest rates of TC in all countries where data
are available.
between ethnic groups.
 New Zealand is the only example where the
non-white population have a higher incidence of
TC than the ‘white’ population living in the same
country.
 The pattern of Pacific Island and Asian rates
being less than European/Other men is
consistent with findings from elsewhere.
 We found an inverse association between
 High socioeconomic status has also been

found to be a risk factor for TC in many studies.
 There is some evidence that the
epidemiological patterns of TC may be different
in New Zealand.

Study Objective
To test whether trends in testicular cancer
incidence have varied by ethnicity and
socioeconomic position in New Zealand
between 1981 and 2004.
Methods
 Cohorts of the entire New Zealand population





for 1981-86, 1986-91, 1991-96, 1996-2001,
2001-2004 were created from Census data and
probabilistically linked to cancer records from
the New Zealand Cancer Registry.
The NZ Cancer Registry is a population-based
registry that collects data on the full population
of New Zealand on all malignant tumours
(except some skin cancers).
Men aged between 15-44 yr were included in
the study.
Testicular cancer (ICD code C62) was
identified from the Cancer Registry.
There are four main ethnic groups in NZ; 1)
the indigenous people (Maori); 2) those of
European origin; 3) People from the Pacific
region and 4) the Asian group.
Household equivalised income was calculated
and assigned to each individual using a NZ
specific equivalisation index, and divided into
tertiles.
Analysis
 Incidence rates, rate ratios and rate
differences (and 95% confidence intervals)
were calculated after direct standardisation of
the cohorts to the age structure of the 2001
WHO population.
 For the income-related calculations, we also
adjusted for ethnicity.
 Statistical tests of trends were conducted for
rates, rate differences and of the log
transformed rate ratios.


 We found increasing rates of TC for all ethnic
groups since 1990s.
 Maori had higher rates, and Pacific and Asian
men had lower rates than European/ Other
men.
 Rate ratios pooled over time were Maori: 1.51
(95% CI 1.31-1.74); Pacific 0.40 (95% CI 0.260.61) and Asian 0.54 (95% CI 0.34-0.94)
compared with European/Other men .


socioeconomic status and testicular cancer rates
even after adjusting for ethnicity.
Most but not all studies have found that men in
high socioeconomic groups have an increased
risk of testicular cancer.
There is also some evidence in the literature that
the historical pattern by SE may be reversing in
some countries, consistent with the NZ findings.
Why differing incidence rates and trends by
social groups?
Diagnostic variation over time or between
social groups. Unlikely to account for these
findings.
Environmental exposures. These are likely to
be important in TC aetiology. Considerable
attention has been paid to antenatal, early life
and peripubertal exposures, but no specific
exposure has yet been identified to explain these
patterns.
Genetic factors: while there is a genetic
component to TC, it is unlikely that genetic
variation alone is sufficient to account for striking
patterns and trends over time for TC,
Key strength: this was
a rare opportunity to
simultaneously link
ethnic and household
income to testicular
cancer records for an
entire country to
estimate trends over
time.
Key limitation: Not all
eligible records could
be linked to the
census, but we
adjusted for linkage
bias using weights, and
we are confident that
residual bias is
minimal.
Conclusions
 There was little evidence of an income-related
association (standardised for ethnicity) with
TC during the 1980s.
 Rates of TC appeared to increase in all
income groups from the early 1990s onwards,
with a relative increase in incidence of 32%,
46% and 51% for men in high, middle and low
income groups respectively.
 The pooled rate ratio comparing low to high
income men was 1.23 (95% CI 1.05-1.44).
1. Maori men have considerably higher rates
of testicular cancer than any other ethnic
group in New Zealand. In all other
countries, white men have the highest risk,
although it is not clear why this is the case.
2. We also found an inverse association
between household income and testicular
cancer rates in contrast to the usual
patterns seen historically.
3. The unusual trends and patterns identified
in the New Zealand context may provide
some aetiological clues for testicular cancer,
but novel ideas are required to identify
specific factors for future investigation.
Sarfati D, Shaw C, Blakely T, Atkinson J, Stanley J. Ethnic and Socioeconomic trends in testicular
cancer incidence in New Zealand. International Journal of Cancer. 2011: 128; 1683-91.