Beskæftigelsesudvalget 2021-22
BEU Alm.del Bilag 317
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Carcinogenicity of occupational exposure as a firefighter
In June, 2022, 25 scientists from
eight countries met at the International
Agency for Research on Cancer (IARC)
in Lyon, France, to finalise their
evaluation of the carcinogenicity of
occupational exposure as a firefighter.
This assessment will be published in
Volume 132 of the
IARC Monographs.
1
Occupational exposure as a firefighter
was classified as “carcinogenic to
humans” (Group 1) based on “sufficient”
evidence for cancer in humans. The
Working Group concluded that there
was “sufficient” evidence in humans
for mesothelioma and bladder cancer.
There was “limited” evidence in humans
for colon, prostate, and testicular
cancers, and for melanoma and non-
Hodgkin lymphoma. There was also
“strong” mechanistic evidence that
occupational exposure as a firefighter
shows the following key characteristics
of carcinogens in exposed humans:
“is genotoxic”, “induces epigenetic
alterations”, “induces oxidative stress”,
“induces chronic inflammation”,
and “modulates receptor-mediated
effects”. Evidence regarding cancer
in experimental animal models was
“inadequate” because no studies were
available. The Group 1 evaluation for
occupational exposure as a firefighter
should be presumed to apply to all
firefighters (including volunteers) and
to both men and women.
Occupational exposure as a
firefighter is complex and includes a
variety of hazards resulting from fires
and non-fire events. Firefighters can
have diverse roles, responsibilities,
and employment (eg, full-time, part-
time, or volunteer) that vary widely
across countries and change over
their career. Firefighters respond to
various types of fires (eg, structure,
wildland, and vehicle fires) and other
events (eg, vehicle accidents, medical
incidents, hazardous material releases,
and building collapses). Wildland
fires are increasingly encroaching on
urban areas. Changes in the types
of fires, building materials, personal
protective equipment (PPE), and roles
and responsibilities among firefighters
have resulted in substantial changes in
firefighter exposures over time.
Firefighters can be exposed to
combustion products from fires
(eg, polycyclic aromatic hydrocarbons
[PAHs] and particulates), building
materials (eg, asbestos), chemicals in
firefighting foams (eg, perfluorinated
and polyfluorinated substances
[PFAS]), flame retardants, diesel
exhaust, and other hazards (eg, night
shift work and ultraviolet or other
radiation). Uptake of fire effluents
or other chemicals can occur via
inhalation and dermal absorption and
possibly via ingestion. Firefighters rely
on PPE to reduce their exposures. Self-
contained breathing apparatus is often
worn during firefighting activities
involving structures or vehicles,
but less commonly during wildland
firefighting, where firefighters can be
deployed to wildfires multiple times
a year and remain near the fire for
several weeks. Dermal absorption of
chemicals can occur even in firefighters
wearing PPE due to limitations
of its design, fit, maintenance, or
decontamination. Furthermore,
exposures can occur when firefighters
are not actively fighting fires and are
not wearing PPE.
Since the previous classification of
firefighting (as “possibly carcinogenic
to humans,” Group 2B) by the
IARC Monographs
in 2007,
2
many
new studies have investigated the
association between occupational
exposure as a firefighter and cancer
risk in humans. A total of 52 cohort
and case-control studies, 12 case
reports, and seven meta-analyses were
considered in the present evaluation.
The Working Group also did a meta-
analysis that incorporated cohort
studies of firefighters published up
to June, 2022. More than 30 non-
overlapping cohort studies following
firefighters for cancer over time were
considered most informative for the
evaluation and were conducted in
Asia, Europe, North America, and
Oceania.
3–5
On the basis of the available
epidemiological evidence, the
Working Group concluded that a
causal association exists between
occupational exposure as a firefighter
and mesothelioma and bladder
cancer. Seven studies examining
mesothelioma incidence among
firefighters were included in the meta-
analysis. For these combined studies,
the Working Group meta-analysis
estimated a 58% higher risk (95% CI
14–120%) for mesothelioma among
firefighters compared with mostly
general populations. Heterogeneity
in the estimate was low across the
group of studies (I²=8%). Asbestos
exposure in firefighting is a plausible
causal agent to support the observed
associations. Confounding by sources
of exposure outside of firefighting,
and other biases, were considered
unlikely to explain the magnitude and
consistency of study results.
Positive associations for bladder
cancer incidence were observed
consistently in several cohort studies
of firefighters compared mostly
with the general population. In the
Working Group’s meta-analysis of
ten studies, the increased risk estimate
was small in magnitude (16%) but
was statistically precise and had low
heterogeneity (95% CI 8–26%,
I²=0).
This estimate was consistent with
two additional higher-quality cohort
studies of cancer incidence that used a
slightly expanded definition of bladder
cancer, and with the results from
studies of bladder cancer mortality.
Further, negative confounding by
smoking was deemed probable,
because lower risks of lung cancer
among firefighters were observed
in most studies, and could have led
to underestimated associations for
bladder cancer in comparison with
the general population. In one pooled
US cohort study,
4
a positive association
Lancet Oncol
2022
Published
Online
June 30, 2022
https://doi.org/10.1016/
S1470-2045(22)00390-4
For more on the
IARC
Monographs
see https://
monographs.iarc.who.int/
Upcoming meetings
February 28–March 7, 2023:
Volume 133: Anthracene,
2-bromopropane, butyl
methacrylate, and dimethyl
hydrogen phosphite
June 6–13, 2023: Volume 134:
Aspartame, methyleugenol,
and isoeugenol
IARC Monographs Working
Group Members
P A Demers (Canada)—Meeting
Chair; D M DeMarini (USA),
KW Fent (USA); D C Glass
(Australia); J Hansen (Denmark) —
Subgroup Meeting Chairs;
O Adetona (USA);
L E Beane Freeman (USA);
A J Caban-Martinez (USA);
R D Daniels (USA); T R Driscoll
(Australia); J M Goodrich (USA);
J M Graber (USA); M H G Andersen
(Denmark); T L Kirkham (Canada);
K Kjaerheim (Norway); D Kriebel
(USA); A S Long (Canada);
L C Main (Australia); M Oliveira
(Portugal); S Peters (Netherlands);
L R Teras (USA); E R Watkins (UK)
Declaration of interests
All Working Group members
declare no competing interests.
Invited Specialists
JL Burgess (USA)
AA Stec (UK)
PA White (Canada)
Declaration of interests
JLB and PAW received research
funding from the International
Association of Fire Fighters.
AAS received research funding
from the Fire Brigades Union.
Representatives
A Berrington, for the National
Cancer Institute, USA;
KM Navarro, for the National
Institute for Occupational Safety
and Health, USA
Declaration of interests
All Representatives declare no
competing interests.
Observers
C Barul, for the National Institute
of Health and Medical Research
(INSERM), France; A Forrest, for
the United Firefighters of
Winnipeg, Canada
www.thelancet.com/oncology
Published online June 30, 2022 https://doi.org/10.1016/S1470-2045(22)00390-4
1
 BEU, Alm.del - 2021-22 - Bilag 317: Orientering om ny IARC-kræftklassificering af brandslukning, fra beskæftigelsesministeren
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Declaration of interests
AF received compensation from
the International Association of
Fire Fighters and travel support
from the United Fire Fighters of
Winnipeg. All other Observers
declare no competing interests.
IARC Secretariat
L Benbrahim-Tallaa;
P Boucheron; A de Conti;
NL DeBono (Co-Responsible
Officer); F El Ghissassi; Y Grosse;
B Hosseini; J Kim; F Madia;
H Mattock;
MK Schubauer-Berigan
(Responsible Officer); LT Stayner;
E Suonio; S Viegas; R Wedekind;
H Zahed
Declaration of interest
All secretariat declare no
competing interests.
For the
Preamble to the IARC
Monographs
see https://
monographs.iarc.who.int/wp-
content/uploads/2019/07/
Preamble-2019.pdf
For
IARC declarations of
interests
see https://
monographs.iarc.who.int/wp-
content/uploads/2021/03/
Participants_Meeting_132.pdf
Disclaimer
The views expressed are those of
the authors and do not
necessarily represent the
decisions, policy, or views of their
respective institutions
in exposure-response analyses with
adjustment for employment duration
suggested that healthy-worker
survivor bias might have attenuated
associations in other studies that
had no such adjustment. Firefighters’
exposures to known and suspected
human bladder carcinogens (eg, PAHs
and soot) were considered plausible
causal agents to support the observed
associations for bladder cancer.
Credible positive associations were
observed for colon, prostate, and
testicular cancers, and for melanoma
and non-Hodgkin lymphoma, based
on estimates from the cohort studies
included in the meta-analysis and
consideration of the larger body of
evidence. However, bias from greater
medical surveillance and detection
in firefighters, or confounding by
physical and lifestyle characteristics
could not be reasonably excluded as
explanations for the positive findings.
Concerns about surveillance bias were
particularly salient for more commonly
indolent or screened cancers such
as prostate and colon, which were
supported by the observation of
attenuated or null associations in
studies of mortality versus incidence.
For some of these cancer types, high
heterogeneity in the meta-analysis
estimates, inconsistent positive
findings from informative studies,
or little evidence for firefighting
exposures known to be associated
with these cancer types also reduced
confidence in a causal conclusion.
For these reasons, a determination
of “limited” evidence was reached for
these five cancer types.
The human cancer evidence for all
other cancer types was “inadequate”,
including for lung and thyroid cancers.
Lung cancer incidence and mortality
rates were lower among firefighters
than in the general population in
most studies and in the meta-analysis;
negative confounding by smoking
and healthy worker hire bias were
presumed to be likely. Surveillance
bias was considered a probable
explanation for the higher incidence
rate of thyroid cancer observed in
firefighters compared with the general
population.
The evaluation of the mechanistic
evidence was based on exposures
associated with fighting structure and
wildland fires, and on employment as
a firefighter. Consistent and coherent
evidence of genotoxic effects was
observed in firefighters: an increase
in the frequency of PAH-DNA adducts
was found in blood; increases in
urinary mutagenicity, DNA damage
in blood, and micronucleus frequency
in buccal cells were associated with
firefighting-related exposures.
Genotoxicity was also observed
in relevant experimental systems:
organic extracts of combustion
emissions relevant to firefighting
exposure increased the frequency of
micronuclei in a human cell line and
of mutations in bacteria. Evidence
of epigenetic effects was observed
in firefighters, based on changes in
blood DNA methylation at loci in
cancer-related genes. Epigenome-
wide association studies among
firefighters showed persistent
changes in DNA methylation asso-
ciated with proxies for cumulative
exposure and DNA methylation
alterations associated either with
years of service or with blood PFAS
concentrations. Exposure-related
alterations in the expression of
microRNAs associated with cancer
were also observed in the blood of
firefighters. Occupational exposure as
a firefighter induced exposure-related
oxidative DNA damage in blood and
oxidative stress markers in urine.
Acute and persistent inflammation
was observed in firefighters.
Airway and systemic inflammatory
markers, such as IL-6 and IL-8, were
associated with firefighting-related
exposures. Moreover, declines in lung
function associated with changes in
inflammatory markers and exposure-
associated bronchial hyperreactivity
were reported in firefighters. A
minority of the Working Group
considered the evidence for chronic
inflammation to be only suggestive;
however, the majority considered the
evidence consistent and coherent for
this key characteristic. Consistent and
coherent evidence was found that
occupational exposure as a firefighter
modulates receptor-mediated effects,
as showb by the activation of the aryl
hydrocarbon receptor.
JLB, AAS, and PAW report research funding from
firefighters’ unions. All other authors declare no
competing interests.
Paul A Demers, David M DeMarini,
Kenneth W Fent, Deborah C Glass,
Johnni Hansen, Olorunfemi Adetona,
Maria HG Andersen,
Laura E Beane Freeman,
Alberto J Caban-Martinez,
Robert D Daniels, Timothy R Driscoll,
Jaclyn M Goodrich, Judith M Graber,
Tracy L Kirkham, Kristina Kjaerheim,
David Kriebel, Alexandra S Long,
Luana C Main, Marta Oliveira,
Susan Peters, Lauren R Teras,
Emily R Watkins; Jefferey L Burgess,
Anna A Stec, Paul A White,
Nathan L DeBono,
Lamia Benbrahim-Tallaa,
Aline de Conti, Fatiha El Ghissassi,
Yann Grosse, Leslie T Stayner,
Eero Suonio, Susana Viegas,
Roland Wedekind, Pauline Boucheron,
Bayan Hosseini, Joanne Kim,
Hana Zahed, Heidi Mattock,
Federica Madia,
Mary K Schubauer-Berigan
International Agency for Research on Cancer, Lyon,
France
1
International Agency for Research on Cancer.
Volume 132: Occupational exposure as a
firefighter. Lyon, France; June 7–14, 2022.
IARC Monogr Identif Carcinog Hazards Hum
(in press).
International Agency for Research on Cancer.
Painting, firefighting, and shift work.
IARC Monogr Identif Carcinog Risks Hum
2010;
98:
1–804.
Glass DC, Pircher S, Del Monaco A, Hoorn SV,
Sim MR. Mortality and cancer incidence in a
cohort of male paid Australian firefighters.
Occup Environ Med
2016;
73:
761–71.
Pinkerton L, Bertke S, Yiin J, et al. Mortality in a
cohort of US firefighters from San Francisco,
Chicago and Philadelphia: an update.
Occup Environ Med
2020;
77:
84–93.
Marjerrison N, Jakobsen J, Demers PA, et al.
Comparison of cancer incidence and mortality
in the Norwegian Fire Departments Cohort,
1960–2018.
Occup Environ Med
2022;
oemed-2022-108331.
2
3
4
5
2
www.thelancet.com/oncology
Published online June 30, 2022 https://doi.org/10.1016/S1470-2045(22)00390-4