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ORIgInAl ARTICle

Long-term follow-up for cancer incidence in a cohort

of Danish ireighters

Kajsa Kirstine Ugelvig Petersen,

Julie elbaek Pedersen,

Jens Peter Bonde,

niels erik ebbehoej,

Johnni Hansen

►

Additional material is

published online only. To view

please visit the journal online

(http://dx.doi.org/10.1136/

oemed-2017-104660).

The Danish Cancer Society

Research Center, The Danish

Cancer Society, Copenhagen,

Denmark

Department of Occupational

and environmental Medicine,

Copenhagen University Hospital

Bispebjerg, Copenhagen,

Denmark

correspondence to

Kajsa Kirstine Ugelvig Petersen,

The Danish Cancer Society

Research Center, The Danish

Cancer Society, Copenhagen,

Denmark; [email protected]

Received 19 July 2017

Revised 29 September 2017

Accepted 12 October 2017

AbstrAct

Objectives

To examine cancer incidence among Danish

ireighters using several employment-related exposure

subgroups.

Methods

A historical cohort of 9061 male Danish

ireighters was established from collected personnel

and membership records from employers and trade

unions. Using the unique Danish personal identiication

number, information on additional previous employment,

cancer and vital status was linked to members of the

cohort from the Supplementary Pension Fund Register,

the Danish Cancer Registry and the Danish Civil

Registration System. SIRs were calculated for speciic

cancer types using rates for the general population,

a sample of the working population and military

employees, respectively.

results

Compared with the selected reference groups,

the overall observed incidence of cancer among the

ireighters was at level with the expected (SIR 1.02,

95% CI 0.96 to 1.09 vs the general population). The SIR

for colon cancer was consistently signiicantly reduced,

while the slight excess seen for melanoma of the skin,

prostate and testicular cancer compared with the general

population was not reproduced using the military as

reference.

conclusions

Previous associations with melanoma of

the skin, prostate and testicular cancer are supported

by our main results. However, the increase in incidence

of these cancers is not reproduced using the military as

reference. Similarities in cancer proile for the ireighters

and the military point to shared risk factors in either

lifestyle or work environment.

What this paper adds

►

Previous studies on cancer incidence among

ireighters have indicated a possible

occupational association for especially

non-Hodgkin’s lymphoma, melanoma, prostate

and testicular cancer.

►

We examined a cohort of 9061 Danish

ireighters using the general population

and two alternative occupational groups as

reference and found no overall increase in

cancer incidence. While a slight excess of

melanoma of the skin, prostate and testicular

cancer was seen among the ireighters

compared with the general population, the

incidence of these cancers was not increased

using the military as reference.

►

The observed similarities in cancer proile for

the ireighters and military employees point to

shared aetiological factors in either work or way

of life. In consequence, focus on factors other

than ire smoke should also be emphasised in

future research.

IntrOductIOn

Where there is fire there is smoke and depending

on the material burning and conditions for combus-

tion, fire smoke contains particles, vapour and

gasses in a complex mixture of chemicals offering

a hostile and dangerous environment to firefighters

working in it. Common components of fire smoke

thus include known human carcinogens such as

benzene, polycyclic aromatic hydrocarbons (PAH),

polychlorinated biphenyls (PCB), asbestos, arsenic,

1,3-butadiene, formaldehyde and cadmium, but the

spectrum of toxic substances and metabolites poten-

tially present in especially structural or vehicle fires

is vast and often unpredictable.

In addition, chem-

icals from extinguishing agents, exhaust gasses and

pollution spills add to the overall exposure load of

firefighters affecting the body after inhalation, oral

and dermal uptake. Furthermore, firefighters are

to cite:

Kirstine Ugelvig

Petersen K, Pedersen Je,

Bonde JP,

et al.

Occup Environ Med

Published

Online First: [please include

Day Month Year]. doi:10.1136/

oemed-2017-104660

intermittently subjected to extreme thermal, phys-

ical and emotional stress and night work.

Evidence of excess cancer morbidity and mortality

among firefighters has been gathered for decades.

In 2007, the International Agency for Research

on Cancer (IARC) conducted a meta-analysis

reviewing 42 existing studies in the field classifying

firefighting as being possibly carcinogenic (group

2B).

At this point, the main suspicion centred on

non-Hodgkin’s lymphoma, prostate and testicular

cancer as the affected outcomes. However, as subse-

quent studies of firefighters almost consistently

report increased risk of malignant melanoma, this

is a cause for concern as well.

2–7

Weakening the evidence of a possible association,

many of the available studies are limited on both

measures of exposure and outcome. Thus, lacking

detailed individual measurement data, duration of

employment normally serves as a proxy for expo-

sure despite uncertainty in the correlation with

actual toxic effects.

Regarding outcomes, only few

countries have access to information from reliable

long-term national cancer registries. Hence, data

from death certificates have frequently been used

yielding only measures of mortality and therefore

impeding evaluation of cancer types with high long-

term survival.

Kirstine Ugelvig Petersen K,

et al. Occup Environ Med

2017;0:1–7. doi:10.1136/oemed-2017-104660

BEU, Alm.del - 2017-18 - Bilag 73: Invitation til teknisk gennemgang af resultaterne fra forskningsprojekterne om brandmænds udsættelse for partikler den 17. januar 2018, fra beskæftigelsesministeren

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The aim of this study is to examine the incidence of specific

cancers among Danish firefighters using national registries of

high quality, and hereby differentiate risk according to several

employment-related exposure parameters. Cancers previously

associated with firefighting will be of a priori interest, namely

melanoma of the skin, non-Hodgkin's lymphoma, prostate and

testicular cancer.

and birth year, was chosen as an image of the working popu-

lation. Second, all men ever employed by the Danish military

were selected as a group resembling the firefighters regarding

both socioeconomic status and physical fitness. Apart from fire-

fighting employment, these additional reference groups were

shaped according to the same criteria as the cohort securing a

sample of 247 350 employees and 391 735 military men.

MAterIAls And MethOds

establishing the cohort

The Danish fire services operate on two main levels. First, a

national level consisting of a governmental emergency agency

with regional departments ensuring local training and assistance.

Second, a municipal level run either by the municipality itself or

contracted out to a private or voluntary fire brigade.

In Denmark, no centralised records exist regarding fire-

fighters. Thus, all both municipal, private and volunteer-based

Danish fire departments along with trade unions and authorities

were contacted initially to retrieve systematic individual employ-

ment information from personnel and membership records. All

permanent residents in Denmark alive on or after 2 April 1968

have by law been awarded a unique personal identification

number (CPR number) by the Danish Civil Registration System

(CRS) containing information on sex and date of birth.

In addi-

tion to this CPR number, basic career data such as employment

types, periods, places and functions were collected for past and

present firefighters. Finally, people stating their job title as fire-

fighter in the CRS were included as well.

Further employment history for the identified firefighters

was extracted from the Danish Supplementary Pension Fund

this register has kept information permanently on all employ-

ment on company and industry type level by wage earners aged

16–66 years working at least 9 hours/week.

Based on these data,

unidentified periods of firefighting employment were added

to cohort members and previously established periods were

confirmed. Combining all retrieved employment records, all

municipal districts in Denmark were represented in the cohort.

exposure

As no single measure could reflect all aspects of firefighting,

several proxies for exposure were assessed in this study. Thus,

duration of firefighting employment (<1 year, ≥1 year, ≥10

years, ≥20 years), era of first employment (pre-1970, 1970

–1994, post-1994), age at first employment (<25 years, ≥25 to

<35 years, ≥35 years), employment type (full time, other) and

function (regular, specialised) were divided into multiple expo-

sure subcategories.

In Denmark, the majority of the larger urban areas employ full-

time career firefighters, whereas rural zones are covered mainly

by part time or volunteer workers. While the roles of especially

volunteer firefighters differ between and within countries, the

ones included in this study were selected for duty with the same

criteria, received the same basic training and education and ulti-

mately performed the same tasks as the part-time workers. In

consequence, the volunteer and part-time firefighters were anal-

ysed together as one group.

Firefighters with multiple employment types were classified

as full time if they had ever been such. Justifying this simplifica-

tion, almost all (99.7%) full-time workers had spent half or more

of their time in this type of employment. In addition, a unit of

specialised smoke divers were analysed separately as a potential

heavy exposure group based on their extensive fire attendance.

Vital status and cancer

Through linkage of CPR numbers to the CRS, vital status,

including date of emigration, disappearance or death, was

obtained for all cohort and reference group members.

Similarly, all cancers diagnosed in Denmark since 1943 have

been registered systematically with almost complete coverage

by the Danish Cancer Registry. Hence, information on specific

cancer types and date of diagnosis was retrieved for the cohort

and reference groups using their CPR numbers.

Follow-up for

cancer started on the latest of either date of first employment or

2 April 1968 for the cohort. It ended on date of death, emigra-

tion or 31 December 2014, whichever came first. All primary

cancers diagnosed within this window of time were included in

the analyses using the ICD-10 (International Classification of

Diseases) system.

study population

With initial evaluation of the collected data records, 17 134 fire-

fighters were identified. Using name, sex, birthdate and work-

place, 1254 firefighters missing a CPR number were tracked in

the CRS adding numbers for 980 of them unambiguously.

Firefighter records were subsequently examined and only

those adhering to all of the cohort criteria were included in the

analyses (valid CPR number, valid employment dates confirmed

by sources containing both past and present employees, date

of birth no earlier than 2 April 1928, firefighting employment

before the age of 60 and 31 December 2004, no diagnoses of

cancer prior to entering firefighting employment and a job title/

function indicating actual firefighting exposure).

Finally, the number of female firefighters identified was

insufficient for meaningful cancer analyses and they were thus

excluded from the cohort (n=316). For further details on the

process of shaping the cohort, see online supplementary figure 1.

statistical analysis

Person-years at risk were calculated for each firefighter according

to the follow-up period and split into 5-year age and calendar

time intervals. Using incidence rates for the entire Danish male

population as reference, the expected number of site-specific

cancers was then calculated according to the same intervals.

Finally, SIRs with corresponding 95% CIs were estimated as

the overall number of observed versus expected cases. This

procedure was repeated comparing the firefighters with the two

external reference groups.

Further, lag time analyses deferring start of follow-up (5,

10, 15 and 20 years) and analyses combining several exposure

measures were performed (online supplementary tables S1,

reference groups

Due to hiring requirements, firefighters may have a better

baseline health than the general population. Thus, in order to

minimise a potential healthy hire effect, two additional external

reference groups were constructed using data from the ATP First,

a sample of all types of employees, selected merely based on sex

Kirstine Ugelvig Petersen K,

et al. Occup Environ Med

2017;0:1–7. doi:10.1136/oemed-2017-104660

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table 1

Characteristics of the cohort of male Danish ireighters:

1968–2014

characteristics

Cohort

Fireighters eligible for SIR analysis

Person-years of follow-up

Mean years of follow-up (SD)

Mean attained age† (SD)

Mean birth year

Vital status†

Alive

Dead

Emigrated

Fireighter employment

Mean age at irst hire (SD)

Average year of irst hire

Year of initial employment

<1970

1970–1994

>1995

Employment duration

<1 year

≥1 year

≥10 years

≥20 years

Average employment length in years (SD)

Job function

Regular

Specialised

*Other comprises part-time/volunteer workers.

†31 December 2014.

3766

477

4818

1102

3141

2541

1711

16 (13.57)

321

4497

3012

1311

14 (10.45)

1186

2196

861

176

2325

2317

26 (5.67)

1979

31 (7.88)

1991

3484

712

4501

291

4243

131 773

31 (11.40)

59 (12.88)

1954

4818

108 772

23 (9.45)

53 (11.50)

1961

Full time

Other*

S4 and S5). Internal analyses were performed using a Poisson

regression model adjusting for age and calendar time.

Approximately 94% of the firefighters were included in the

cohort from sources with complete employment records from

the beginning of the follow-up period in 1968. In order to assess

the remaining potential left truncation, a sensitivity analysis

restricting the cohort to firefighters born after 31 December

1949 was performed (online supplementary table S2).

As the lag time, internal and sensitivity analyses contributed

no substantial additional information, only the main results of

the external analyses are presented here.

Statistical analyses were conducted using Stata V

.14.2

(StataCorp, College Station, TX, USA).

For melanoma of the skin, an increase was seen compared

with both the general population and the sample of employees

reaching significance for the latter. The SIR for firefighters

employed before the age of 25 was significantly increased using

both these reference groups (SIR 1.46, 95% CI 1.07 to 2.02 and

SIR 1.55, 95% CI 1.13 to 2.14) while the SIR for specialised fire-

fighters was significantly increased versus all three references.

The incidence of non-melanoma skin cancer was overall near

expectation.

A slight excess of prostate cancer was observed in compar-

ison to the general population. This excess bordered significance

against the sample of employees, while disappearing almost

with the military as reference. Regarding the selected exposure

measures, no distinct pattern of risk correlation seemed present

(table

3).

As for age at diagnosis, a significant increase in pros-

tate cancer was seen ≥70 years while younger age groups (<50

years) had less than expected cases.

The SIR for testis cancer was increased compared with the

general population (SIR 1.30, 95% CI 0.97 to 1.73). A slight

excess was seen in the group aged 50–69 at diagnosis (SIR 1.17,

95% CI 0.40 to 2.73), while the majority of cases occurred

before the age of 50 (online supplementary table S3). The overall

excess was, however, not reproduced using the additional refer-

ence groups. Finally, the distribution of cases regarding histolog-

ical subtypes did not differ from that of the general population

(data not shown). The incidence of non-Hodgkin's lymphoma

was at level with all three references (table

2).

The only outcome with significantly increased SIR across all

references was cancer of the heart and mediastinum with only

three cases. In contrast, the incidence of colon cancer was signifi-

cantly reduced versus all references (table

2).

There were also

slightly less than expected cases of lung cancer compared with

the general population or the sample of employees.

For the lymphohaematopoietic cancers, the only outcome

showing excess was Hodgkin’s lymphoma. The SIR for

Hodgkin’s lymphoma was significantly increased for part-time/

volunteer firefighters (SIR 2.29, 95% CI 1.15 to 4.58; general

population), firefighters employed after 1994 or for minimum

of 1 year increasing with longer employment duration.

Among the remaining sites analysed, pancreatic cancer was the

only outcome with more than one significantly increased SIR

across the selected exposure subgroups (full-time firefighters,

first employed before 1970 and hired before the age of 25).

dIscussIOn

With this first large cohort study of cancer incidence among

male Danish firefighters, 51 cancer sites are evaluated through

46 years of follow-up in relation to several exposure measures.

Overall cancer morbidity is almost at level with that of the

general population and the two additional reference groups.

However, the pattern of excess, regarding specific cancer types

generated by previous studies in this field, is in part confirmed.

For melanoma of the skin, the observed modest increase is

consistent with findings from the meta-analysis by LeMasters

and numerous subsequent studies.

2–7 11

Ultraviolet (UV) radia-

tion is the predominant risk factor involved in carcinogenesis of

the skin and receiving excessive amounts is often work or life-

style related. While the cumulative life dose of UV light primarily

affects the risk of non-melanoma skin cancer, the incidence of

melanoma seems closely related to early, intermittent and intense

exposures. When working outdoors though, firefighters are typi-

cally completely covered by protective gear and clothing limiting

their occupational exposure to sunlight.

results

The final cohort consisted of 9061 male Danish firefighters

contributing 240 545 person-years at risk. At the end of follow-up,

7985 were living in Denmark, 1003 were deceased and 73 had

emigrated. The mean attained age at the end of follow-up was

59 years for the full-time employees versus 53 years among the

part-time/volunteer workers.

Table 1

summarises the selected

characteristics of the cohort.

In total, 1389 primary cancers were observed among 1211

firefighters during follow-up. Compared with the general popu-

lation, the overall cancer incidence was almost even (SIR 1.02,

95% CI 0.96 to 1.09). There were, however, notable differ-

ences in the incidence of specific cancer types.

Table 2

presents

the results by reference group.

Kirstine Ugelvig Petersen K,

et al. Occup Environ Med

2017;0:1–7. doi:10.1136/oemed-2017-104660

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table 2

Cancer incidence among 9061 male Danish ireighters by reference group: 1968–2014

the general population

cancer site (Icd-10)

All cancers (minus other skin)

Lip (C00)

Tongue (C01–02)

Mouth (C03–06, C462)

Salivary glands (C07–08)

Pharynx (C09–14)

Oesophagus (C15)

Stomach (C16)

Colon (C18–19)

Rectum (C20)

Liver (C22)

Gall bladder (C23–24)

Pancreas (C25)

Anus (C21, C26)

Nasal cavity (C30–31)

Larynx (C32)

Lung (C33–34, C39)

Heart and mediastinum (C380–383, C388)

Bones (C40–41)

Melanoma of skin (C43)

Other skin (C44, C460)

Mesothelium (C450–459)

Connective tissue

Prostate (C61)

Testis (C62)

Other genitals (C60, C63)

Kidney (C64)

Renal pelvis (C65–66)

Urinary bladder (C67, D090, D303, D414)

Eye (C69)

Meninges (C70, D32, D42)

Brain (C71, C751–753, D330–332, D430–432, D352–

354, D443–445)

Other parts of CNS (C72, D333–339, D433–D439)

Thyroid (C73)

Hodgkin’s lymphoma (C81)

Non-Hodgkin’s lymphoma (C82–85, C883–889)

Myeloma (C90, C880–882)

Lymphatic leukaemia (C91)

Myeloid leukaemia (C92)

Ill-deined/unspeciied (C76–80)

Remaining not shown

Obs

1071

132

318

202

sIr

1.02

1.04

1.52

0.60

1.79

0.91

0.99

1.09

0.73

1.22

0.97

0.99

1.20

1.31

1.38

0.92

0.91

4.27

1.25

1.24

1.00

0.65

0.84

1.10

1.30

0.78

1.04

1.46

1.09

0.88

1.22

0.94

1.39

1.21

1.64

0.96

0.62

0.91

0.76

0.90

0.41

95% cI

0.96 to 1.09

0.39 to 2.78

0.86 to 2.68

0.28 to 1.25

0.67 to 4.77

0.59 to 1.41

0.65 to 1.53

0.75 to 1.59

0.57 to 0.95

0.95 to 1.55

0.58 to 1.64

0.41 to 2.37

0.86 to 1.68

0.49 to 3.49

0.52 to 3.67

0.56 to 1.50

0.76 to 1.07

1.38 to 13.23

0.40 to 3.89

0.98 to 1.57

0.90 to 1.12

0.24 to 1.73

0.40 to 1.76

0.95 to 1.26

0.97 to 1.73

0.25 to 2.41

0.74 to 1.47

0.79 to 2.72

0.89 to 1.35

0.28 to 2.74

0.64 to 2.35

0.67 to 1.33

0.79 to 2.45

0.54 to 2.69

0.95 to 2.82

0.69 to 1.32

0.31 to 1.24

0.55 to 1.51

0.40 to 1.46

0.62 to 1.32

0.13 to 0.97

sample of employees

sIr

1.07

1.13

1.62

0.57

1.90

0.94

1.05

1.12

0.77

1.24

0.98

1.04

1.27

1.13

1.27

0.92

0.95

3.61

1.17

1.28

1.01

0.68

0.97

1.15

1.04

0.82

1.02

1.59

1.11

0.82

1.07

0.87

1.47

1.18

1.35

0.97

0.66

0.97

0.73

0.95

0.42

95% cI

1.01 to 1.14

0.42 to 3.01

0.92 to 2.85

0.27 to 1.19

0.71 to 5.07

0.60 to 1.45

0.68 to 1.61

0.77 to 1.63

0.59 to 0.99

0.97 to 1.58

0.58 to 1.65

0.43 to 2.50

0.91 to 1.78

0.42 to 3.01

0.48 to 3.39

0.57 to 1.51

0.80 to 1.13

1.17 to 11.20

0.38 to 3.64

1.01 to 1.61

0.90 to 1.12

0.26 to 1.82

0.46 to 2.04

1.00 to 1.32

0.78 to 1.39

0.26 to 2.54

0.72 to 1.44

0.85 to 2.95

0.90 to 1.37

0.27 to 2.55

0.56 to 2.05

0.62 to 1.23

0.83 to 2.58

0.53 to 2.63

0.78 to 2.32

0.70 to 1.33

0.33 to 1.32

0.59 to 1.61

0.38 to 1.40

0.65 to 1.38

0.14 to 0.97

the military

sIr

1.01

1.60

1.46

0.61

1.59

0.87

1.18

1.26

0.70

1.20

1.17

1.02

1.28

1.12

1.42

1.01

1.06

4.30

1.14

1.05

0.86

0.71

0.77

1.02

0.98

0.70

1.04

1.35

1.05

0.90

1.23

0.90

1.31

1.05

1.42

0.97

0.65

0.88

0.83

0.96

0.41

95% cI

0.95 to 1.07

0.60 to 4.28

0.83 to 2.57

0.29 to 1.27

0.60 to 4.24

0.56 to 1.35

0.77 to 1.81

0.87 to 1.84

0.54 to 0.90

0.94 to 1.53

0.69 to 1.98

0.42 to 2.44

0.92 to 1.80

0.42 to 2.99

0.53 to 3.79

0.62 to 1.66

0.90 to 1.26

1.39 to 13.32

0.37 to 3.55

0.83 to 1.33

0.77 to 0.96

0.27 to 1.89

0.37 to 1.61

0.88 to 1.17

0.73 to 1.30

0.23 to 2.18

0.74 to 1.48

0.73 to 2.51

0.86 to 1.30

0.29 to 2.78

0.64 to 2.37

0.64 to 1.26

0.74 to 2.30

0.47 to 2.35

0.82 to 2.44

0.70 to 1.34

0.33 to 1.31

0.53 to 1.47

0.43 to 1.60

0.66 to 1.40

0.13 to 0.95

CNS, central nervous system; ICD, International Classiication of Diseases.

Among the chemicals encountered occupationally by fire-

fighters, a causal relation to melanoma of the skin has been

shown for PCBs and is suspected for other relevant exposures

potentially entering the body through dermal uptake such as

PAHs and dioxins.

12 13

Supporting a potential occupational asso-

ciation, the incidence of melanoma is significantly increased

among the specialised firefighters in our cohort. However, the

differences observed between the regular firefighters and this

elite unit may also be explained by lifestyle and in particular

tanning fashions.

We also observe a slight excess in the incidence of prostate

cancer, though neither overall nor subgroup results reach signif-

icance. Our results show fewer than expected cases among

firefighters under 50 years of age and a significant increase in

later ages countering the tendency of an increased incidence in

younger age groups (30–49 years) seen in recent studies.

5 14

In Denmark, full-time firefighters work mainly 24-hour shifts

while part-time and volunteer personnel have more varied shift

structures. Night shift work has been linked to increased risk of

prostate cancer by previous studies and interestingly, comparing

firefighters with other potential night workers such as our

military reference shows virtually no difference in incidence.

However, our military reference generally seems to resemble the

firefighters closely regarding cancer incidence and apart from

having similar occupational conditions, they may share life-

style-related confounders.

Kirstine Ugelvig Petersen K,

et al. Occup Environ Med

2017;0:1–7. doi:10.1136/oemed-2017-104660

Kirstine Ugelvig Petersen K,

et al. Occup Environ Med

2017;0:1–7. doi:10.1136/oemed-2017-104660

table 3

Cancer incidence among male Danish ireighters by exposure subgroup compared with the general population: 1968–2014

employment type

Full time (n=4243)

cancer site*

All cancers (minus other skin)

Colon

Rectum

Pancreas

Lung

Melanoma of the skin

Other skin

Prostate

Testis

Urinary bladder

Non-Hodgkin's lymphoma

Obs

680

180

130

Job function

regular (n=8584)

cancer site

All cancers (minus other skin)

Colon

Rectum

Pancreas

Lung

Melanoma of the skin

Other skin

Prostate

Testis

Urinary bladder

Non-Hodgkin's lymphoma

Obs

994

125

287

188

sIr (95% cI)

1.02 (0.96 to 1.08)

0.73 (0.56 to 0.96)

1.18 (0.91 to 1.53)

1.17 (0.83 to 1.67)

0.92 (0.77 to 1.09)

1.15 (0.90 to 1.48)

0.97 (0.86 to 1.09)

1.09 (0.95 to 1.26)

1.27 (0.94 to 1.71)

1.10 (0.89 to 1.37)

0.91 (0.65 to 1.29)

specialised (n=477)

Obs

sIr (95% cI)

1.12 (0.88 to 1.39)

0.78 (0.29 to 2.08)

1.72 (0.77 to 3.84)

1.60 (0.52 to 4.97)

0.73 (0.35 to 1.54)

2.44 (1.27 to 4.70)

1.49 (1.04 to 2.11)

1.15 (0.68 to 1.94)

1.65 (0.62 to 4.39)

0.95 (0.39 to 2.28)

1.53 (0.57 to 4.08)

sIr (95% cI)

1.06 (0.99 to 1.15)

0.79 (0.58 to 1.08)

1.16 (0.84 to 1.60)

1.54 (1.05 to 2.25)

0.87 (0.70 to 1.08)

1.28 (0.94 to 1.74)

0.96 (0.83 to 1.11)

1.12 (0.95 to 1.33)

1.23 (0.82 to 1.86)

1.14 (0.89 to 1.48)

1.02 (0.68 to 1.53)

Other† (n=4818)

Obs

391

138

sIr (95% cI)

0.96 (0.87 to 1.06)

0.64 (0.40 to 1.01)

1.31 (0.89 to 1.92)

0.65 (0.31 to 1.37)

0.97 (0.73 to 1.27)

1.19 (0.83 to 1.70)

1.07 (0.90 to 1.26)

1.05 (0.83 to 1.32)

1.36 (0.91 to 2.04)

1.01 (0.70 to 1.45)

0.87 (0.52 to 1.47)

era of irst employment

<1970 (n=1362)

Obs

521

126

108

sIr (95% cI)

1.12 (1.02 to 1.22)

0.78 (0.55 to 1.11)

1.47 (1.06 to 2.02)

1.63 (1.08 to 2.48)

0.99 (0.79 to 1.24)

1.42 (0.96 to 2.11)

0.97 (0.81 to 1.15)

1.16 (0.96 to 1.40)

1.55 (0.77 to 3.09)

1.21 (0.92 to 1.59)

0.90 (0.52 to 1.55)

1970–1994 (n=4521)

Obs

455

159

sIr (95% cI)

0.93 (0.85 to 1.02)

0.73 (0.49 to 1.09)

1.01 (0.68 to 1.51)

0.78 (0.42 to 1.45)

0.80 (0.60 to 1.06)

1.07 (0.76 to 1.51)

1.04 (0.89 to 1.21)

1.05 (0.85 to 1.30)

1.32 (0.91 to 1.91)

1.05 (0.75 to 1.46)

0.89 (0.56 to 1.42)

≥1995 (n=3178)

Obs

sIr (95% cI)

1.04 (0.84 to 1.27)

0.40 (0.10 to 1.59)

0.80 (0.26 to 2.49)

1.02 (0.26 to 4.08)

0.88 (0.42 to 1.85)

1.43 (0.83 to 2.47)

0.98 (0.70 to 1.38)

0.90 (0.47 to 1.73)

1.12 (0.62 to 2.02)

0.41 (0.10 to 1.66)

1.46 (0.65 to 3.24)

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Age at irst employment

<25 years (n=4016)

Obs

572

132

100

sIr (95% cI)

1.12 (1.03 to 1.22)

0.85 (0.60 to 1.19)

1.13 (0.79 to 1.63)

1.68 (1.12 to 2.53)

0.95 (0.75 to 1.20)

1.47 (1.07 to 2.02)

0.89 (0.75 to 1.05)

1.12 (0.92 to 1.36)

1.33 (0.90 to 1.97)

1.32 (1.01 to 1.73)

0.83 (0.50 to 1.37)

25–34 years (n=3426)

Obs

286

117

sIr (95% cI)

0.91 (0.81 to 1.03)

0.59 (0.34 to 1.02)

1.25 (0.80 to 1.96)

0.36 (0.12 to 1.13)

0.78 (0.55 to 1.10)

0.77 (0.47 to 1.28)

1.18 (0.98 to 1.41)

1.08 (0.83 to 1.41)

1.21 (0.75 to 1.94)

0.76 (0.47 to 1.22)

1.21 (0.73 to 2.00)

≥35 years (n=1619)

Obs

213

sIr (95% cI)

0.95 (0.83 to 1.09)

0.65 (0.36 to 1.18)

1.36 (0.83 to 2.22)

1.27 (0.63 to 2.53)

0.97 (0.68 to 1.38)

1.52 (0.95 to 2.45)

0.99 (0.78 to 1.26)

1.06 (0.80 to 1.42)

1.48 (0.62 to 3.56)

0.98 (0.61 to 1.58)

0.86 (0.41 to 1.80)

employment duration

<1 year (n=1423)

cancer site

All cancers (minus other skin)

Colon

Rectum

Pancreas

Lung

Melanoma of the skin

Other skin

Prostate

Testis

Urinary bladder

Non-Hodgkin's lymphoma

Obs

318

sIr (95% cI)

1.14 (1.02 to 1.27)

0.70 (0.43 to 1.14)

1.08 (0.66 to 1.77)

1.79 (1.05 to 3.01)

1.13 (0.85 to 1.49)

1.07 (0.62 to 1.85)

0.82 (0.65 to 1.05)

1.12 (0.87 to 1.45)

1.72 (0.92 to 3.19)

1.28 (0.90 to 1.82)

0.86 (0.43 to 1.73)

≥1 year (n=7638)

Obs

753

252

143

sIr (95% cI)

0.98 (0.91 to 1.06)

0.75 (0.55 to 1.02)

1.27 (0.96 to 1.68)

0.98 (0.63 to 1.52)

0.81 (0.65 to 1.00)

1.28 (0.99 to 1.66)

1.06 (0.94 to 1.20)

1.09 (0.92 to 1.28)

1.22 (0.88 to 1.68)

1.01 (0.78 to 1.32)

0.98 (0.68 to 1.42)

≥10 years (n=5553)

Obs

615

219

125

sIr (95% cI)

0.94 (0.87 to 1.02)

0.82 (0.60 to 1.12)

1.16 (0.85 to 1.60)

0.74 (0.43 to 1.27)

0.73 (0.57 to 0.93)

1.19 (0.88 to 1.60)

1.09 (0.96 to 1.25)

1.09 (0.91 to 1.29)

1.07 (0.73 to 1.59)

1.04 (0.79 to 1.37)

0.93 (0.62 to 1.40)

≥20 years (n=3022)

Obs

447

159

101

sIr (95% cI)

0.91 (0.83 to 1.00)

0.84 (0.59 to 1.20)

1.32 (0.94 to 1.85)

0.74 (0.40 to 1.37)

0.70 (0.53 to 0.93)

0.96 (0.64 to 1.43)

1.08 (0.92 to 1.26)

1.12 (0.92 to 1.36)

0.99 (0.58 to 1.67)

0.97 (0.70 to 1.34)

0.88 (0.54 to 1.43)

Workplace

*Results for overall cancer and the 10 most frequent cancer sites shown.

†Other comprises part-time/volunteer workers.

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Workplace

For testis cancer, the pattern of accordance with the military

reference continues with a SIR of 0.98. The corresponding SIR

versus the general population is 1.30 (95% CI 0.97 to 1.73). In

spite of a significant relative risk of 1.47 (95% CI 1.20 to 1.80)

in the meta-analysis by IARC, recent studies have shown no

consistency in results regarding this outcome.

1–7 14 16–18

Though

testicular cancer worldwide is a relatively rare disease, Denmark

has one of the highest national incidence rates. Confirmed aeti-

ological factors are related mainly to early life events, while

possible associations with exposures from lifestyle, environment

or occupation remain hypothetical.

In our cohort, the highest

risk of testicular cancer is seen among the short-term firefighters

(<1 year of employment) and in the youngest age group (<50

years), and the histological distribution is similar to that of the

general population limiting support for the hypothesised associ-

ation with firefighting.

The incidence of non-Hodgkin's lymphoma in our cohort is

near expectation. In the meta-analysis by IARC building on 7

studies and 312 cases, this outcome is significantly increased.

However, only few of the subsequent large studies support this

finding.

2 16

As the contrasting excess of Hodgkin’s lymphomas

observed in our cohort is significant only among the presum-

ably less exposed part-time/volunteer workers, this may not be

work related.

Previous studies on a small cohort of Danish firefighters have

shown significant increases in both lung cancer incidence and

death.

5 20

Despite possible exposure to inhalable combustion

products, the incidence of lung cancer is not increased in our

cohort. However, assessing the impact of firefighting on this

particular outcome is difficult without knowledge of smoking

habits for both cohort and reference groups. The overall inci-

dence of tobacco-related cancers (mouth, tongue, pharynx,

larynx, nasal cavity, lung, oesophagus, pancreas, stomach, colon,

rectum, liver, kidney, renal pelvis, urinary bladder, myeloid

leukaemia) in our cohort is at level with that of the general popu-

lation though (SIR 0.98, 95% CI 0.90 to 1.07).

The significant reduction in colon cancer observed in our

study is generally not seen in previous studies.

Notably, rectum

cancer shares many risk factors connected to this outcome and

no reduction is seen here (table

2).

Though the incidence of

pancreatic cancer is increased for several exposure subgroups,

the increase seems confined to short-term firefighters limiting

suspicion of an occupational association.

Finally, the significant increase in cancer of the heart and

mediastinum is likely a random finding. Thus, the three observed

cases each represent different and rare cancers with the only

common denominator being the anatomical location in the chest.

As for limitations in our study, potential confounders related

to non-firefighting jobs or lifestyle such as smoking, alcohol

consumption, diet and sun exposure may affect the incidence of

certain cancers. Despite the long follow-up period, the cohort

is relatively young leaving the number of detected cancers

low and infrequent types difficult to evaluate. Further, cancer

among female firefighters cannot be assessed in this study, as

the number of women in this profession, at least in Denmark,

remains negligible. Lastly, the selected surrogate measures

may not reflect actual exposure as well as the number, type

and duration of runs or fires fought, which have been tested

in recent studies.

3 21

As fires are dictated by circumstance in an

uncontrolled and unpredictable manner, fire attendance varies

greatly between firefighters limiting the use of employment

parameters as proxies for exposure to smoke.

In defence of

our approach, firefighters typically spend little time at fires

and other sources of occupational hazards (night work, exhaust

gasses from traffic) may correlate better with employment

measures.

Keeping the limited number of firefighters in Denmark in

mind, the established cohort is relatively large covering a wide

span of firefighting history with long follow-up. In addition,

occupational information is confirmed by multiple sources vali-

dating the chosen measures of exposure. Another important

strength is the use of different reference groups addressing the

presence of a potential healthy worker effect in the cohort.

Finally, the old and virtually complete national health regis-

tries offer accurate and valid information on both cancer and

vital status. Reliable calculation of cancer incidence is thus

possible even in early eras of firefighting.

cOnclusIOn

The overall incidence of cancer is not increased among the fire-

fighters in our cohort, but the previously seen increase in the

incidence of melanoma of the skin, prostate and testicular cancer

is supported by our main results. However, the slight excess

observed for all three cancer sites is reduced notably using mili-

tary employees as reference. The observed similarities in cancer

profile for these two occupational groups point to shared aeti-

ological factors in either work or way of life. In consequence,

focus on factors other than fire smoke should also be emphasised

in future research.

Continued follow-up of the cohort is recommended and

planned in order to provide further clarity on the association

between firefighting and cancer morbidity.

Acknowledgements

The authors would like to thank the involved ire services

and trade unions for providing the necessary data used in the study.

contributors

KKUP collected the data, performed programming and analyses,

participated in interpretation of results and wrote the manuscript. JeP performed

programming of data, participated in analyses and interpretation of results, and

revised the manuscript critically. JPB and nee designed the study, supervised

the interpretation of results and revised the manuscript critically. JH was a major

contributor in designing the study and supervised all subsequent data collection,

programming and analyses, participated in interpretation of results and supervised

writing of the manuscript. JH was responsible for guaranteeing the overall content.

All authors read and approved the inal manuscript.

Funding

The study was funded by a grant from the Danish Working environment

Research Fund.

competing interests

none declared.

Provenance and peer review

not commissioned; externally peer reviewed.

expressly granted.

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Long-term follow-up for cancer incidence in a

cohort of Danish firefighters

Kajsa Kirstine Ugelvig Petersen, Julie Elbaek Pedersen, Jens Peter

Bonde, Niels Erik Ebbehoej and Johnni Hansen

Occup Environ Med

published online October 21, 2017

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