Comments on Hardell and Carlberg Increasing Rates of Brain Tumors in the Swedish National Inpatient Register and the Causes of Death Register. Int. J. Environ. Res. Public Health 2015, 12, 3793-3813

Abstract

Hardell and Carlberg claim in a recent article that both the Cause of Death Register and the National Inpatient Care Register indicate that there was a severe and increasing underreporting of malignant brain tumors to the Swedish Cancer Register during recent years [1]. [...].

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Int. J. Environ. Res. Public Health 2015, 12, 11662-11664; doi:10.3390/ijerph120911662
International Journal of
Environmental Research and
Public Health
ISSN 1660-4601
www.mdpi.com/journal/ijerph
Comment
Comments on Hardell and Carlberg Increasing Rates of Brain
Tumors in the Swedish National Inpatient Register and the
Causes of Death Register. Int. J. Environ. Res. Public Health
2015, 12, 3793–3813
Anders Ahlbom
1,
*, Maria Feychting
1
, Lars Holmberg
2
, Lars Age Johansson
3
,
Tiit Mathiesen
4,5
, David Pettersson
1
, Joachim Schüz
6
and Mats Talbäck
1
1
Institute of Environmental Medicine, Karolinska Institutet, P.O. Box 210, SE-171 77 Stockholm,
Sweden; E-Mails: maria.feychting@ki.se (M.F.); david.h.pettersson@ki.se (D.P.);
mats.talback@ki.se (M.T.)
2
Regional Cancer Center, Uppsala/Örebro and The National Board of Health and Welfare, SE-112
59 Stockholm, Sweden; E-Mail: lars.holmberg@akademiska.se
3
Nordic Collaborating Centre for Classifications in Health Care, P.O. Box 7000, St. Olavs Pass,
NO-0130 Oslo, Norway; E-Mail: lars.age@bredband.net
4
Department of Clinical Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden; E-
Mail: tiit.mathiesen@karolinska.se
5
Neurosurgery Clinic at the Karolinska University Hospital, SE-171 76 Solna, Sweden
6
Section of Environment and Radiation, International Agency for Research on Cancer, 150 Cours
Albert Thomas, 69372 Lyon, France; E-Mail: SchuzJ@iarc.fr
* Author to whom correspondence should be addressed; E-Mail: anders.ahlbom@ki.se;
Tel.: +46-703-247-470.
Academic Editor: Paul B. Tchounwou
Received: 1 June 2015 / Accepted: 11 September 2015 / Published: 17 September 2015
Hardell and Carlberg claim in a recent article that both the Cause of Death Register and the
National Inpatient Care Register indicate that there was a severe and increasing underreporting of
malignant brain tumors to the Swedish Cancer Register during recent years [1]. As a consequence,
they claim, the Swedish Cancer Register fails to report that malignant brain tumor incidence rates have
in fact increased since 2007/2008. They suggest that this increase might be due to an increasing
exposure to the population from radiofrequency electromagnetic fields emanating from mobile
communications.
OPEN ACCESS

Int. J. Environ. Res. Public Health 2015, 12 11663
Their claim is based on the observation that tumors of unknown type in the brain or CNS (ICD10
D43) in both the Cause of Death Register and the National Inpatient Care Register have been
increasing since 2007/2008. There are several problems with the authors’ use of these data, one of
which is displayed in Figure 1. The figure shows age-standardized death rates for malignant brain
tumors (ICD10 C71) in the middle line and brain and CNS tumors of unknown type in the bottom line.
The top line displays the sum of the two lower lines. Two things are obvious from the figure. First, the
two lower lines are closely related and one goes up when the other goes down. Second, the trend for
the two diagnostic categories taken together is flat. That is, the Cause of Death Register does not
indicate that malignant brain tumors have been increasing during recent years and the claim by the
authors is simply not correct. The basis for their conclusion is the rise of the death rates for D43 from
2008 and onwards, at an annual rate of 22%. The real explanation to this trend is readily available in a
reference from the Register [2]. The explanation is that the Register decided to speed up the
registration process by making fewer requests for more detailed information by accepting the coding of
more tumors as unspecified type but with no effect on the total number of brain tumors.
Figure 1. Age standardized mortality rates from the Swedish Cause of Death Register.
The results that are presented from the National Inpatient Care Register are based on hospital
discharges retrieved from tables published by the National Board of Health and Welfare and not
relevant for analysis of cancer incidence trends. The coverage rate of the Swedish Cancer Register
has been examined by means of a comparison with data extracted from the register of hospital
discharges [3]. A substantial underreporting was found for tumors of the central nervous system for
ages above 70 years (44% for men and 30% for women). The underreporting for men and women
below the age of 70 was however modest, 5.5 and 7.1% respectively. Upon scrutiny of medical
records, it was found that over 50% of tumors that were reported to the hospital discharge registry
during 1998, but were not found in the cancer register during the same year, should not have been
reported to the cancer register. The main reasons were that it was not cancer or it was cancer, but the
tumor should not be included as an incident case for the year evaluated. For the underreporting to hide

Int. J. Environ. Res. Public Health 2015, 12 11664
a trend in cancer incidence it would have to get bigger with time, but no information is available
about this.
Although the figures that are presented in the article may well be correct, their interpretation is
grossly misleading. Already the title is misleading because the rates of brain tumor are not increasing
in the Cause of Death Register. The reason for the rise of the subtype of brain and CNS tumor rates of
unknown type is known and documented in the open literature. The authors actually mention
themselves the close correlation between the trends of the unspecified and the malignant tumors in the
Cause of Death Register, but choose to disregard it in their interpretation of data.
References
1. Hardell, L.; Carlberg, M. Increasing rates of brain tumours in the Swedish national inpatient
register and the causes of death register. Int. J. Environ. Res. Public Health 2015, 12, 3793–3813.
2. National Board of Health and Welfare. Causes of Death 2010; National Board of Health and
Welfare: Stockholm, Sweden, 2011; p. 24.
3. Barlow, L.; Westergren, K.; Holmberg, L.; Talback, M. The completeness of the Swedish Cancer
Register: A sample survey for year 1998. Acta Oncol. 2009, 48, 27–33.
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