EPIDEMIOLOGY
Breast cancer incidence trends in European women aged
20–39 years at diagnosis
D. F. Merlo
•
M. Ceppi
•
R. Filiberti
•
V. Bocchini
•
A. Znaor
•
M. Gamulin
•
M. Primic-Z
ˇ
akelj
•
P. Bruzzi
•
C. Bouchardy
•
A. Fucic
•
AIRTUM WG
Received: 6 January 2012 / Accepted: 12 March 2012 / Published online: 29 March 2012
Springer Science+Business Media, LLC. 2012
Abstract
An increase in the incidence of breast cancer in
women aged
\
40 years has been reported in recent years.
Increased incidence could be partly explained by subtle
detection biases, but the role of other risk factors cannot be
ruled out. The purpose of the present study was to inves-
tigate the changes in temporal trends in breast cancer
incidence in European women aged 20–39 years at diag-
nosis. Age specific breast cancer incidence rates for 17
European Cancer Registries were retrieved for the calendar
period 1995–2006. Cancer registries data were pooled to
reduce annual fluctuations present in single registries and
increase incidence rates stability. Regression models were
fitted to the data assuming that the number of cancer cases
followed the Poisson distribution. Mean annual changes
in the incidence rate (AIC) across the considered time
window were calculated. The AIC estimated from all
European registries was 1.032 (95 % CI
=
1.019–1.045)
and 1.014 (95 % CI
=
1.010–1.018) in women aged 20–29
and 30–39 years old at diagnosis, respectively. The major
change was detected among women aged 25–29 years at
diagnosis: AIC
=
1.033 (95 % CI
=
1.020–1.046). The
upward trend was not affected when registries with high or
low AIC were removed from the analysis (sensitivity
analysis). Our findings support the presence of an increase
in the incidence of breast cancer in European women in
their 20s and 30s during the decade 1995–2006. The
interpretation of the observed increase is not straightfor-
ward since a number of factors may have affected our
results. The estimated annual increase in breast cancer
incidence may result in a burden of the disease that is
important in terms of public health and deserves further
investigation of possible risk factors.
Keywords
Breast cancer
Incidence
Time trend
Young women
Introduction
Breast cancer is the most common form of cancer in
women in most parts of the world, especially in the
industrialized areas [
1
]. In Europe, it accounts for about
30 % of all incident tumors in females [
2
], with rates
ranging from about 40/100,000 in Lithuania and Poland, to
75/100,000 in Norway, and to over 90/100,000 in the
Netherlands and some Italian areas [
3
]. Overall, the annual
breast cancer incidence had been increasing worldwide
during the last century [
4
–
6
], but a downturn in tumor
incidence was observed in the 2,000s among women older
than 45–50 years at diagnosis in the United States, possibly
The members of AIRTUM Working Group are given in Appendix.
D. F. Merlo (
&
)
M. Ceppi
R. Filiberti
V. Bocchini
P. Bruzzi
IRCCS AOU San Martino-IST-Istituto Nazionale per la Ricerca
sul Cancro, Genoa, Italy
e-mail: franco.merlo@istge.it
A. Znaor
Croatian National Cancer Registry, Zagreb, Croatia
M. Gamulin
Clinical Hospital Centre Zagreb, Zagreb, Croatia
M. Primic-Z
ˇ
akelj
Cancer Registry of Republic of Slovenia, Ljubljana, Slovenia
C. Bouchardy
Geneva Cancer Registry, Geneva, Switzerland
A. Fucic
Institute for Medical Research and Occupational Health, Zagreb,
Croatia
123
Breast Cancer Res Treat (2012) 134:363–370
DOI 10.1007/s10549-012-2031-7
in relation to the decrease in the use of hormone replace-
ment therapy [
7
,
8
], and in some European countries [
9
–
13
]
In the meantime, a number of European cancer registries
had started to report an upward trend, since the 1990s,
among women aged
\
40 years. The average annual
increase between 1995 and 2004 ranged between 2 % in
the Eindhoven cancer registry, south eastern Netherlands
[
14
] and 8.7 % in the Canton of Geneva where a particu-
larly marked increase (46.7 %) was observed during the
triennium 2002–2004 [
15
]. In general, these registry spe-
cific statistics are based on small numbers of cases per year
observed in young women, with an inevitable high degree
of variability and should be interpreted with caution.
However, the increase of 1.3 % per year in invasive breast
cancer incidence between 1992 and 2004 among US white
women younger than 40 years at diagnosis is based on
large number of cases and cannot be considered as the
result of a chance fluctuation [
16
].
The aim of this study was to investigate the existence in
Europe of a recent increase in the incidence of invasive
breast cancer in women aged
\
40 years at diagnosis by
exploring age-specific temporal trends in pooled incident
data from European population-based cancer registries.
Methods
Data from 17 European population-based registries that
had uninterrupted registration for at least 5 years over the
period 1995–2006 were used to evaluate overall and age-
specific incidence changes of invasive breast cancer in
women aged 20–39 years at diagnosis. Yearly based breast
cancer incident cases were available on a national basis for
12 registries and referred to cities or counties for the others
(Table
1
). Data were extracted between October and
December 2009 from the registry websites for the registries
of Belgium, Czech Republic, Ireland, the Netherlands,
Scotland, Bremen, Saarland, and Schleswig–Holstein. The
database of the Association of the Nordic Cancer Registries
(NORDCAN) [
17
] was used to retrieve incidence data for
the Danish, Finnish, Icelandic, Norwegian, and Swedish
registries. Incidence data were directly provided for the
Cancer Registry of Croatia, Slovenia, and Geneva (Swit-
zerland). The Italian Association of Cancer Registries
(AIRTUM) provided data for the county registries of
Modena, Parma, Reggio Emilia, and Naples. Data were
available for the following periods: 1995–2006 for the
registries of Croatia, Denmark, Finland, Geneva, Iceland,
Table 1
European cancer registries demographic items, and website
Registry Identifier Female
population*
Population coverage Website
Belgian Cancer Registry Belgium 1,425,726 Belgium
http://www.kankerregister.org
Bremen Cancer Registry Bremen 91,462 Land Bremen (DE)
http://www.krebsregister.bremen.de
Croatian National Cancer
Registry
Croatia 634,590 Republic of Croatia
http://www.hzjz.hr/cancer
Czech National Cancer
Registry
Czech 1,511,081 Czech Republic
http://www.uzis.cz
Danish Cancer Registry Denmark 740,151 Denmark
http://www.ancr.nu/nordcan.asp
Finnish Cancer Registry Finland 667,779 Republic of Finland
http://www.ancr.nu/nordcan.asp
Geneva Cancer Registry Geneve 65,578 Canton of Geneva (CH)
http://www.asrt.ch
Icelandic Cancer Registry Iceland 41,626 Republic of Iceland
http://www.ancr.nu/nordcan.asp
The Irish National Cancer
Registry
Ireland 593,666 Republic of Ireland
http://www.ncri.ie
Italian Cancer Registries Italy 290,711 4 Italian areas**
http://www.registri-tumori.it
National Netherlands Cancer
Registry
Netherlands 2,310,413 The Netherlands
http://www.ikcnet.nl
Cancer Registry of Norway Norway 630,346 Norway
http://www.ancr.nu/nordcan.asp
Cancer Registry Saarland Saarland 140,952 Land Saarland (DE)
http://www.krebsregister.saarland.de
Cancer Registry Schleswig–
Holstein
Schleswig–Holstein 359,088 Land Schleswig–Holstein (DE)
http://www.krebsregister-sh.de
Scottish Cancer Registry Scotland 729,841 Scotland
http://www.isdscotland.org
Cancer Registry of Slovenia Slovenia 292,055 Republic of Slovenia
http://www.onko-i.si
Swedish Cancer Registry Sweden 1,159,781 Sweden
http://www.ancr.nu/nordcan.asp
* Age group 20–39
** Counties of Parma, Modena, Reggio Emilia, and Naples’ Local Health Unit 4
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