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1492
CORRESPONDENCE
Increased Incidence Rates but No
Space–Time Clustering of Childhood
Astrocytoma in Sweden, 1973–1992
A Population-Based Study of Pediatric Brain Tumors
W
e read with interest the report of Hjalmars et al., documenting an
increase in childhood brain cancer incidence in Sweden for the
period 1973–1992.1 The authors note average annual increases of 2.6%
for this period, with the increase restricted to the astrocytoma category and not noted for either the primitive neuroectodermal tumor
(PNET)/medulloblastoma subcategory or the ependymoma subcategory.
The incidence of brain cancers among children younger than 15
years in the United States also increased during this time period, with
an average annual increase of 1.8% from 1973 to 1994.2 We have
presented a detailed analysis of the temporal trend for this increase in
brain cancer incidence among children in the U.S.3 We demonstrated
that this increase was best explained by a model with a step increase
in incidence occurring in the mid-1980s (termed the “jump model”),
compared with the alternative model of a continuous increase in
incidence from 1973 to 1994. Similar to the data for Swedish children,
the increase in brain cancer incidence for children in the U.S. from
the 1970s to the 1990s was restricted to the astrocytoma subcategory,
with no increase observed for the PNET/medulloblastoma subcategory.4 The significantly better fit of the incidence data by the jump
model (in the absence of a jump in mortality rates) supports the
hypothesis that the observed increase in incidence somehow resulted
from changes in detection (e.g., the availability of magnetic resonance
imaging for brain imaging in the mid 1980s) and/or the reporting of
childhood primary malignant brain tumors during the mid 1980s.3,5
Subsequent to our initial analysis demonstrating the superior fit
of the jump model to the continuous increase model, data for childhood brain cancer incidence for 1995 and 1996 have become available, which provide further support for the jump model.6 These most
recent incidence data from the SEER program document essentially
stable brain cancer incidence rates among children in the U.S. since
1986 (with an estimated annual percentage change of 0.2%).6 In
addition, the California Cancer Registry recently reported that brain
cancer rates for children in California were essentially constant for the
years 1988 –1995 (with an estimated annual percentage change of
⫺1.7%, P ⬎ 0.05).7
Visual inspection of the temporal trends in childhood brain cancer incidence presented by Hjalmars et al. suggest that the “jump
model” may be applicable to their data for children in Sweden.1 For
example, visual inspection of the incidence pattern for all malignant
brain tumors (Fig. 2b in their article), for the astrocytoma subcategory
(Fig. 2c), and for the astrocytoma subcategory among girls (Fig. 2e)
© 2000 American Cancer Society
Correspondence
suggests a possible demarcation between lower stable
rates prior to the mid 1980s compared with higher
stable rates after the mid-1980s.
It would be of great interest to analyze the brain
cancer incidence data for children in Sweden for its fit
to the jump model (including incidence data for years
subsequent to 1992, if these are available). These analyses would demonstrate whether the jump model with
stable incidence rates since the mid-1980s applies for
childhood brain cancer incidence in Sweden as it does
in the U.S.
7.
1493
SEER cancer statistics review, 1973–1996, NIH Pub. No. 992789. Bethesda, MD: National Cancer Institute, 1999.
Campleman S, Perkins C, Schlag R. Incidence patterns of
childhood brain cancer in California. North American Association of Central Cancer Registries: Annual Meeting, April
8, 1999.
Malcolm A. Smith, M.D., Ph.D.
Brois Freidlin, Ph.D.
Lynn A. G. Ries, M.S.
Richard Simon, D.Sc.
National Cancer Institute
Bethesda, Maryland
REFERENCES
1.
2.
3.
4.
5.
6.
Hjalmars U, Kulldorff M, Wahlqvist Y, Lannering B. Increased incidence rates but no space–time clustering of
childhood astrocytoma in Sweden, 1973–1992: a population-based study of pediatric brain tumors. Cancer 1999;85:
2077–90.
Ries L, Kosary C, Hankey B, Miller B, Harras A, Edwards B.
SEER cancer statistics review, 1973–1994, NIH Pub. No. 972789. Bethesda, MD: National Cancer Institute, 1997.
Smith M, Freidlin B, Ries L, Simon R. Trends in reported
incidence of primary malignant brain tumors in children in
the United States. J Natl Cancer Inst 1998;90:1269 –77.
Linet MS, Ries LA, Smith MA, Tarone RE, Devesa SS. Cancer
surveillance series: recent trends in childhood cancer incidence and mortality in the United States. J Natl Cancer Inst
1999;91:1051– 8.
Black WC. Increasing incidence of childhood primary malignant brain tumors: enigma or no-brainer? [editorial]
J Natl Cancer Inst 1998;90:1249 –51.
Ries L, Kosary C, Hankey B, Miller B, Clegg L, Edwards B.
Author Reply
W
e appreciate Dr. Smith’s comments on our report. As “the jump model” is of great interest, we
are currently conducting a follow-up study of pediatric
brain tumors in Sweden, including an analysis of a
possible step increase of astrocytoma incidence. The
results will be published as soon as possible.
Ulf Hjalmars, M.D.
Department of Paediatrics
Östersunds Hospital
Östersund, Sweden
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