Cancer incidence among firefighters in Seattle and Tacoma, Washington (United States)

Methodological and Practical Challenges in Synthesizing Occupational Cancer Studies

Studies examining occupational exposures and cancer risk frequently report mixed findings; it is thus imperative for researchers to synthesize study results and identify any potential sources that explain such variabilities in study findings. However, when synthesizing study results using meta-analytic techniques, researchers often encounter a number of practical and methodological challenges. These challenges include (1) an incomparability of effect size measures due to large variations in research methodology; (2) a violation of the independence assumption for meta-analysis; (3) a violation of the normality assumption of effect size measures; and (4) a variation in cancer definitions across studies and changes in coding standards over time. In this paper, we first demonstrate these challenges by providing examples from a real dataset collected for a large meta-analysis project that synthesizes cancer mortality and incidence rates among firefighters. We summarize how each of these challenges has been handled in our meta-analysis. We conclude this paper by providing practical guidelines for handling challenges when synthesizing study findings from occupational cancer literature.

Association of firefighting exposures with lung function using a novel job exposure matrix (JEM)

OBJECTIVES

Characterisation of firefighters' exposures to dangerous chemicals in smoke from non-wildfire incidents, directly through personal monitoring and indirectly from work-related records, is scarce. The aim of this study was to evaluate the association between smoke particle exposures (P) and pulmonary function.

METHODS

The study period spanned from January 2010 through September 2021. Routine firefighting P were estimated using fire incident characteristics, response data and emission factors from a novel job exposure matrix. Linear mixed effects modelling was employed to estimate changes in pulmonary function as measured by forced expiratory volume in one second (FEV1). Models controlled for age, race/ethnicity, height, smoking and weight.

RESULTS

Every 1000 kg P was associated with 13 mL lower FEV1 (β=-13.34; 95% CI=-13.98 to -12.70) over the entire 12-year follow-up period. When analysing exposures within 3 months before PFT measurements, 1000 kg P was associated with 27 mL lower FEV1 (β=-26.87; 95% CI=-34.54 to -19.20). When evaluating P estimated within 3 months of a pulmonary function test (PFT), stronger associations were observed among those most highly exposed to the World Trade Center (WTC) disaster (β=-12.90; 95% CI=-22.70 to -2.89); the association of cumulative exposures was similar for both highly and less highly exposed individuals.

DISCUSSION

Smoke particle exposures were observed to have modest short-term and long-term associations with pulmonary function, particularly in those who, previously, had high levels of WTC exposure. Future work examining the association between P and pulmonary function among non-WTC exposed firefighters will be essential for disentangling the effects of ageing, routine firefighting and WTC exposures.

Development of a job-exposure matrix (JEM) for exposure to smoke particle mass among firefighters of the Fire Department of the City of New York (FDNY)

OBJECTIVES

A refined job exposure matrix (JEM) based on incident types and severities and response characteristics was developed for firefighters to estimate quantities of smoke particles emitted during structural and non-structural fire incidents from 2010 to 2021.

METHODS

The cohort included a subset of 3237 Fire Department of the City of New York firefighters who responded to at least one incident between 2010 and 2021, prior to retirement. Fire incident data included dates, type, severity (alarm level) and location. Response data included dates worked, firehouse, position titles and shift lengths for each firefighter. The quantity of smoke particle mass generated during structural and non-structural fires adjusted by individual firefighter engagement was computed using the United States Environmental Protection Agency AP-42 emissions framework. Correlations between years of employment, fire responses and career total particle mass concentration by firefighter were examined. Linear regression models were fit and corresponding R² values were calculated.

RESULTS

Firefighters responded to a median of 424.7 (IQR=202.3-620.0) annual incidents/person; 17.6% were fire incidents (median=77.1; IQR=40.4-114.0). Structural fires were the most common type of fire incident (72.5% of annual incidents/person; median=55.9; IQR=29.6-85.5). Incident severity (alarm level) and firefighter engagement (position title) appeared to differentiate between high and low exposure regimes (R²=0.43). Incident severity explained most of the variability of particle exposures (R²=0.90).

CONCLUSIONS

Using the JEM, job-related smoke particle concentrations were estimated to vary by incident type, incident severity and firefighter engagement, highlighting the importance of using refined measures, so that future studies can more accurately evaluate associations between firefighting and health outcomes.

Comparison of cancer incidence and mortality in the Norwegian Fire Departments Cohort, 1960-2018

OBJECTIVES

Elevated risk of cancer at several sites has been reported among firefighters, although with mixed findings. The purpose of this study was to calculate standardised incidence ratios (SIRs) and standardised mortality ratios (SMRs) for cancer and compare them to assess whether use of the different measures could be a source of inconsistencies in findings.

METHODS

The Norwegian Fire Departments Cohort, comprising 4295 male employees who worked at 15 fire departments across Norway, was linked to health outcome registries for the period 1960-2018. SIRs and SMRs were derived using national reference rates.

RESULTS

Overall, we observed elevated incidence of colon cancer (SIR, 95% CI 1.27, 1.01 to 1.58), mesothelioma (2.59, 1.12 to 5.11), prostate cancer (1.18, 1.03 to 1.34) and all sites combined (1.15, 1.08 to 1.23). Smaller, non-significant elevations were found for mortality of colon cancer (SMR, 95% CI 1.20, 0.84 to 1.67) and mesothelioma (1.66, 0.34 to 4.86), while SMR for prostate cancer was at unity. Potential errors were observed in some of the mortality data, notably for mesothelioma cases. Among those who died of cancer, 3.7% (n=14) did not have a prior diagnosis of malignancy at the same site group.

CONCLUSIONS

Assessment of incidence or mortality did not greatly influence the interpretation of results. The most prominent differences in SIR and SMR appeared to be due to inconsistencies between sites of cancer diagnosis and cause of death. The difference in SIR and SMR for prostate cancer suggested a detection bias from differential screening practices.

Temporal association of prostate cancer incidence with World Trade Center rescue/recovery work

BACKGROUND

The World Trade Center (WTC) attacks on 11 September 2001 created a hazardous environment with known and suspected carcinogens. Previous studies have identified an increased risk of prostate cancer in responder cohorts compared with the general male population.

OBJECTIVES

To estimate the length of time to prostate cancer among WTC rescue/recovery workers by determining specific time periods during which the risk was significantly elevated.

METHODS

Person-time accruals began 6 months after enrolment into a WTC cohort and ended at death or 12/31/2015. Cancer data were obtained through linkages with 13 state cancer registries. New York State was the comparison population. We used Poisson regression to estimate hazard ratios and 95% CIs; change points in rate ratios were estimated using profile likelihood.

RESULTS

The analytic cohort included 54 394 male rescue/recovery workers. We observed 1120 incident prostate cancer cases. During 2002-2006, no association with WTC exposure was detected. Beginning in 2007, a 24% increased risk (HR: 1.24, 95% CI 1.16 to 1.32) was observed among WTC rescue/recovery workers when compared with New York State. Comparing those who arrived earliest at the disaster site on the morning of 11 September 2001 or any time on 12 September 2001 to those who first arrived later, we observed a positive, monotonic, dose-response association in the early (2002-2006) and late (2007-2015) periods.

CONCLUSIONS

Risk of prostate cancer was significantly elevated beginning in 2007 in the WTC combined rescue/recovery cohort. While unique exposures at the disaster site might have contributed to the observed effect, screening practices including routine prostate specific antigen screening cannot be discounted.

Cancer Incidence and Mortality among Firefighters: An Overview of Epidemiologic Systematic Reviews

Firefighters are exposed to carcinogens that may increase their risk of developing many types of occupational cancer. Many systematic reviews (SRs) have been produced with sometimes conflicting conclusions. In this overview of reviews, we aim to assess the conclusion consistency across the available systematic reviews on the cancer risk in firefighters. Literature searches were conducted in several indexed databases and grey literature to retrieve systematic reviews aiming to evaluate cancer incidence or cancer mortality in firefighters. Results from included SRs were analyzed according to the tumour site. Out of 1054 records identified by the search in the databases, a total of 11 SRs were ultimately included. The original studies (n = 104) analyzed in the SRs were published between 1959 and 2018. The results consistently reported a significant increase in the incidence of rectal, prostate, bladder and testicular cancers as well as mesothelioma and malignant melanoma in firefighters compared to the general population. The SRs also indicate that death rates from rectal cancer and non-Hodgkin's lymphoma are higher among firefighters. Consistent SR results suggest that several types of cancer may be more frequent in firefighters than in the general population.

Cancer risks of firefighters: a systematic review and meta-analysis of secular trends and region-specific differences

PURPOSE

The objective of this study was to conduct a systematic review and meta-analysis to evaluate the cancer risks among firefighters in the time course and from different geographical areas.

METHOD

A PubMed search was performed to identify cohort studies about cancer risk and firefighting presented with standardized incidence ratios (SIRs) or standardized mortality ratios (SMRs). Using random-effect models, meta-relative risk estimates (mSIRs, mSMRs) and 95% confidence intervals (CI) were assessed. Cohort studies with employment starting before 1950 were classified as "old", studies starting between 1950 and 1970 as "medium", and later studies as "new".

RESULTS

The general cancer risk of firefighters was similar to the general population, but mSMR decreased over time (new studies: mSMR = 0.81, 95% CI 0.70-0.92). We observed an increase of mSIR for melanoma of the skin and prostate cancer as well as a decrease of mSIR for stomach cancer with later employment onset. For those cancer sites, we did not observe a secular trend of mSMRs. Regional differences between relative cancer risks were particularly observed for bladder cancer.

CONCLUSIONS

Among other things, innovative firefighting techniques and better personal protective equipment have provided a safer and healthier working environment for firefighters over time leading to a reduction of overall cancer incidence and mortality ratios. Increased general preventive medical checkups and possible additional screenings for firefighters might have led to more findings of malignant melanoma of the skin and prostate cancer in the recent past.

Cancer Incidence and Mortality in Firefighters: A State-of-the-Art Review and Meta-َAnalysis

Objective:

A systematic literature review and meta-analysis was conducted on the association between firefighting and cancer.

Methods:

A comprehensive literature search of databases including Medline, EMBASE, Biosis, NIOSHTIC2, Web of Science, Cancerlit, and HealthStar, for the period between 1966 to January 2007, was conducted. We also retrieved additional studies by manual searching.

Results:

A total of 49 studies were included in the meta-analysis. We found statistically significant associations between firefighting and cancers of bladder, brain and CNS, and colorectal cancers, consistent with several previous risk estimates. We also found statistically significant associations of firefighting with non-Hodgkin’s lymphoma, skin melanoma, prostate, and testicular cancer. For kidney, Hodgkin’s lymphoma, leukemia, lymphosarcoma and reticulosarcoma, multiple myeloma, and pancreatic cancer, we found some statistically significant but less consistent results. For all other cancers evaluated (esophageal, laryngeal, oral and pharyngeal, liver and gallbladder, lung, lymphatic and hematopoietic, non-melanoma skin cancer, stomach, and urinary cancer) we did not find any statistically significant associations.

Conclusions:

Although our meta-analysis showed statistically significant increased risks of either cancer incidence or mortality of certain cancers in association with firefighting, a number of important limitations of the underlying studies exist, which, precluded our ability to arrive at definitive conclusions regarding causation.

Cancer incidence and mortality among firefighters

Firefighters are exposed to both known and suspected carcinogens. This study aims to systematically review the literature on the association of firefighting occupation and cancer incidence and mortality, overall and for specific cancer sites. A systematic review using PubMed, Embase, and Web of Science was performed up to January 1, 2018. We extracted risk estimates of cancers and calculated summary incidence risk estimates (SIRE), summary mortality risk estimates (SMRE), and their 95% confidence intervals (CI). Publication bias and risk of bias in individual studies were assessed using Begg's and Egger's tests and the Newcastle-Ottawa scale (NOS), respectively. We included 50 papers in the review and 48 in the meta-analysis. We found significantly elevated SIREs for cancer of the colon (1.14; CI 1.06 to 1.21), rectum (1.09; CI 1.00 to 1.20), prostate (1.15; CI 1.05 to 1.27), testis (1.34; CI 1.08 to 1.68), bladder (1.12; CI 1.04 to 1.21), thyroid (1.22; CI 1.01 to 1.48), pleura (1.60; CI 1.09 to 2.34), and for malignant melanoma (1.21; CI 1.02 to 1.45). We found significant SMREs of 1.36 (1.18 to 1.57) and 1.42 (1.05 to 1.90) for rectal cancer and Non-Hodgkin's lymphoma, respectively. Considering the significantly elevated risk of some cancers in this occupational group, we suggest improving preventive measures and securing adequate and relevant medical attention for this group. Further studies with more accurate and in-depth exposure assessments are indicated.

Prostate cancer in firefighting and police work: a systematic review and meta-analysis of epidemiologic studies

OBJECTIVES

We conducted a systematic review and meta-analysis to evaluate potential associations between firefighting and police occupations, and prostate cancer incidence and mortality.

METHODS

Original epidemiological studies published from 1980 to 2017 were identified through PubMed and Web of Science. Studies were included if they contained specific job titles for ever/never firefighting and police work and associated prostate cancer risk estimates with 95% confidence intervals (CI). Study quality was assessed using a 20-point checklist. Prostate cancer meta-risk estimates (mRE) and corresponding 95% CIs were calculated for firefighting and police work separately and by various study characteristics using random effects models. Between-study heterogeneity was evaluated using the I² score. Publication bias was assessed using Begg's and Egger's tests.

RESULTS

A total of 26 firefighter and 12 police studies were included in the meta-analysis, with quality assessment scores ranging from 7 to 19 points. For firefighter studies, the prostate cancer incidence mRE was 1.17 (95% CI = 1.08-1.28, I² = 72%) and the mortality mRE was 1.12 (95% CI = 0.92-1.36, I² = 50%). The mRE for police incidence studies was 1.14 (95% CI = 1.02-1.28; I² = 33%); for mortality studies, the mRE was 1.08 (95% CI = 0.80-1.45; I² = 0%). By study design, mREs for both firefighter and police studies were similar to estimates of incidence and mortality.

CONCLUSION

Small excess risks of prostate cancer were observed from firefighter studies with moderate to substantial heterogeneity and a relatively small number of police studies, respectively. There is a need for further studies to examine police occupations and to assess unique and shared exposures in firefighting and police work.

Lung Cancer Among Firefighters: Smoking-Adjusted Risk Estimates in a Pooled Analysis of Case-Control Studies

OBJECTIVES

The aim of this study was to explore lung cancer risk among firefighters, with adjustment for smoking.

METHODS

We used pooled information from the SYNERGY project including 14 case-control studies conducted in Europe, Canada, New Zealand, and China, with lifetime work histories and smoking habits for 14,748 cases of lung cancer and 17,543 controls. We estimated odds ratios by unconditional logistic regression with adjustment for smoking and having ever been employed in a job known to present an excess risk of lung cancer.

RESULTS

There was no increased lung cancer risk overall or by specific cell type among firefighters (n = 190), neither before nor after smoking adjustment. We observed no significant exposure-response relationship in terms of work duration.

CONCLUSIONS

We found no evidence of an excess lung cancer risk related to occupational exposure as a firefighter.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

Creation of a retrospective job-exposure matrix using surrogate measures of exposure for a cohort of US career firefighters from San Francisco, Chicago and Philadelphia

OBJECTIVES

To construct a cohort-specific job-exposure matrix (JEM) using surrogate metrics of exposure for a cancer study on career firefighters from the Chicago, Philadelphia and San Francisco Fire Departments.

METHODS

Departmental work history records, along with data on historical annual fire-runs and hours, were collected from 1950 to 2009 and coded into separate databases. These data were used to create a JEM based on standardised job titles and fire apparatus assignments using several surrogate exposure metrics to estimate firefighters' exposure to the combustion byproducts of fire. The metrics included duration of exposure (cumulative time with a standardised exposed job title and assignment), fire-runs (cumulative events of potential fire exposure) and time at fire (cumulative hours of potential fire exposure).

RESULTS

The JEM consisted of 2298 unique job titles alongside 16,174 fire apparatus assignments from the three departments, which were collapsed into 15 standardised job titles and 15 standardised job assignments. Correlations were found between fire-runs and time at fires (Pearson coefficient=0.92), duration of exposure and time at fires (Pearson coefficient=0.85), and duration of exposure and fire-runs (Pearson coefficient=0.82). Total misclassification rates were found to be between 16-30% when using duration of employment as an exposure surrogate, which has been traditionally used in most epidemiological studies, compared with using the duration of exposure surrogate metric.

CONCLUSIONS

The constructed JEM successfully differentiated firefighters based on gradient levels of potential exposure to the combustion byproducts of fire using multiple surrogate exposure metrics.

Risk of cancer among firefighters in California, 1988-2007

BACKGROUND

Most studies of firefighter cancer risks were conducted prior to 1990 and do not reflect risk from advances in building materials.

METHODS

A case-control study using California Cancer Registry data (1988-2007) was conducted to evaluate the risk of cancer among firefighters, stratified by race.

RESULTS

This study identified 3,996 male firefighters with cancer. Firefighters were found to have a significantly elevated risk for melanoma (odds ratio [OR] = 1.8; 95% confidence interval [CI] 1.4-2.1), multiple myeloma (OR 1.4; 95%CI 1.0-1.8), acute myeloid leukemia (OR 1.4; 95%CI 1.0-2.0), and cancers of the esophagus (OR 1.6; 95%CI 1.2-2.1), prostate (OR 1.5; 95%CI 1.3-1.7), brain (OR 1.5; 95%CI 1.2-2.0), and kidney (OR 1.3; 95%CI 1.0-1.6).

CONCLUSIONS

In addition to observing cancer findings consistent with previous research, this study generated novel findings for firefighters with race/ethnicity other than white. It provides additional evidence to support the association between firefighting and several specific cancers.

Exposure-response relationships for select cancer and non-cancer health outcomes in a cohort of U.S. firefighters from San Francisco, Chicago and Philadelphia (1950-2009)

OBJECTIVES

To examine exposure-response relationships between surrogates of firefighting exposure and select outcomes among previously studied US career firefighters.

METHODS

Eight cancer and four non-cancer outcomes were examined using conditional logistic regression. Incidence density sampling was used to match each case to 200 controls on attained age. Days accrued in firefighting assignments (exposed-days), run totals (fire-runs) and run times (fire-hours) were used as exposure surrogates. HRs comparing 75th and 25th centiles of lagged cumulative exposures were calculated using loglinear, linear, log-quadratic, power and restricted cubic spline general relative risk models. Piecewise constant models were used to examine risk differences by time since exposure, age at exposure and calendar period.

RESULTS

Among 19,309 male firefighters eligible for the study, there were 1333 cancer deaths and 2609 cancer incidence cases. Significant positive associations between fire-hours and lung cancer mortality and incidence were evident. A similar relation between leukaemia mortality and fire-runs was also found. The lung cancer associations were nearly linear in cumulative exposure, while the association with leukaemia mortality was attenuated at higher exposure levels and greater for recent exposures. Significant negative associations were evident for the exposure surrogates and colorectal and prostate cancers, suggesting a healthy worker survivor effect possibly enhanced by medical screening.

CONCLUSIONS

Lung cancer and leukaemia mortality risks were modestly increasing with firefighter exposures. These findings add to evidence of a causal association between firefighting and cancer. Nevertheless, small effects merit cautious interpretation. We plan to continue to follow the occurrence of disease and injury in this cohort.

Non-cancer occupational health risks in firefighters

BACKGROUND

Firefighters are exposed to a number of different workplace hazards. As a result of this and the perception of increased ill-health symptoms, a systematic review was carried out to identify significant associations.

AIMS

To carry out a systematic review of evidence relating to non-cancer occupational health risks in firefighters.

METHODS

Systematic literature searches were conducted using a predetermined search strategy that encompassed terms describing the population of interest and health outcomes. Titles and abstracts identified were subjected to an initial screening process using specified guidelines. Included papers were reviewed and data extracted. Additional material, in the form of papers cited by those selected for review, was also obtained and, where relevant, added to the review. Extracted data were then collated into evidence tables to support the narrative review.

RESULTS

Relatively few papers were identified that addressed forms of ill-health in firefighters other than cancer. Nine papers were considered covering each of coronary heart disease and respiratory health. Other ill-health outcomes studied were hearing loss (five studies); hip osteoarthritis (two studies); and sarcoidosis (two studies). None of these sets of papers provided conclusive evidence of a consistent relationship between the specified disease outcomes and the occupation as a firefighter; although, in some instances (hearing loss, respiratory health, and hip and knee osteoarthritis), there were limited indications of some effect.

CONCLUSIONS

None of the sets of papers reviewed showed any consistent association between the occupation of firefighter and any of a number of non-cancer disease and ill-health outcomes.

Mortality and cancer incidence in a pooled cohort of US firefighters from San Francisco, Chicago and Philadelphia (1950-2009)

OBJECTIVES

To examine mortality patterns and cancer incidence in a pooled cohort of 29 993 US career firefighters employed since 1950 and followed through 2009.

METHODS

Mortality and cancer incidence were evaluated by life table methods with the US population referent. Standardised mortality (SMR) and incidence (SIR) ratios were determined for 92 causes of death and 41 cancer incidence groupings. Analyses focused on 15 outcomes of a priori interest. Sensitivity analyses were conducted to examine the potential for significant bias.

RESULTS

Person-years at risk totalled 858 938 and 403 152 for mortality and incidence analyses, respectively. All-cause mortality was at expectation (SMR=0.99, 95% CI 0.97 to 1.01, n=12 028). There was excess cancer mortality (SMR=1.14, 95% CI 1.10 to 1.18, n=3285) and incidence (SIR=1.09, 95% CI 1.06 to 1.12, n=4461) comprised mainly of digestive (SMR=1.26, 95% CI 1.18 to 1.34, n=928; SIR=1.17, 95% CI 1.10 to 1.25, n=930) and respiratory (SMR=1.10, 95% CI 1.04 to 1.17, n=1096; SIR=1.16, 95% CI 1.08 to 1.24, n=813) cancers. Consistent with previous reports, modest elevations were observed in several solid cancers; however, evidence of excess lymphatic or haematopoietic cancers was lacking. This study is the first to report excess malignant mesothelioma (SMR=2.00, 95% CI 1.03 to 3.49, n=12; SIR=2.29, 95% CI 1.60 to 3.19, n=35) among US firefighters. Results appeared robust under differing assumptions and analytic techniques.

CONCLUSIONS

Our results provide evidence of a relation between firefighting and cancer. The new finding of excess malignant mesothelioma is noteworthy, given that asbestos exposure is a known hazard of firefighting.

Evaluation of a bladder cancer cluster in a population of criminal investigators with the Bureau of Alcohol, Tobacco, Firearms and Explosives--part 2: the association of cancer risk and fire scene investigation

This study evaluated the association of bladder cancer risk and fire scene investigation within a cohort of white male criminal investigators with the United States Bureau of Alcohol, Tobacco, Firearms and Explosives that was found to be at increased risk for bladder cancer. Medical surveillance data were used in a nested case-control study to determine odds ratios (ORs) estimating the relative risk of the cancer associated with post-fire investigation. The study comprised seven bladder cancer cases and 1525 controls. Six of the cases reported holding assignments associated with post-fire investigation. The OR for bladder cancer was 19.01 (95% confidence interval = 1.94-186.39) for those holding any one or more of these assignments for one to four years versus zero years and 12.56 (1.14-138.58) for those holding any one or more of these assignments for five or more years versus zero years. The risk for bladder cancer is significantly elevated for those holding post-fire investigation assignments compared to those not holding these assignments.

Night shift work and levels of 6-sulfatoxymelatonin and cortisol in men

BACKGROUND

Night shift work is associated with cancer among men, but the biologic mechanism is unclear. We investigated whether male night shift workers showed changes in levels of melatonin and cortisol, potential biomarkers of cancer risk.

METHODS

Urine was collected from 185 night shift and 158 day shift-working male healthcare providers, aged 22 to 55 years, throughout work and sleep periods, and assayed for 6-sulfatoxymelatonin and cortisol. Morning serum was collected within 90 minutes of completing the night and assayed for cortisol.

RESULTS

Night shift workers had significantly lower 6-sulfatoxymelatonin levels during daytime sleep, nighttime work, and nighttime sleep on off-nights (57%, 62%, and 40% lower, respectively), relative to the day shift workers during nighttime sleep (P < 0.0001); urinary cortisol in night shift workers was 16% higher during daytime sleep and 13% lower during nighttime sleep on off-nights (P < 0.05). Morning serum cortisol post-work and post-sleep in night shift workers were 24% and 43% lower, respectively, than post-sleep levels among day shift workers (P < 0.0001). Within-subject comparisons among the night shift workers revealed significantly lower melatonin levels and significantly higher urinary cortisol levels during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.01); morning serum cortisol levels post-work were lower than those post-sleep.

CONCLUSIONS

Night shift workers have substantially lower 6-sulfatoxymelatonin during night work and daytime sleep, and levels remain low when night shift workers sleep at night. Chronic reduction in melatonin among night shift workers may be an important carcinogenic mechanism. Cortisol secretion patterns may be impacted by night shift work, which could affect cancer risk.

IMPACT

Shift work could be an important risk factor for many types of cancer.

Health consequences of circadian disruption in humans and animal models

Daily rhythms in behavior and physiology are programmed by a hierarchical collection of biological clocks located throughout the brain and body, known as the circadian system. Mounting evidence indicates that disruption of circadian regulation is associated with a wide variety of adverse health consequences, including increased risk for premature death, cancer, metabolic syndrome, cardiovascular dysfunction, immune dysregulation, reproductive problems, mood disorders, and learning deficits. Here we review the evidence for the pervasive effects of circadian disruption in humans and animal models, drawing from both environmental and genetic studies, and identify questions for future research.

Do evolutionary life-history trade-offs influence prostate cancer risk? a review of population variation in testosterone levels and prostate cancer disparities

An accumulation of evidence suggests that increased exposure to androgens is associated with prostate cancer risk. The unrestricted energy budget that is typical of Western diets represents a novel departure from the conditions in which men's steroid physiology evolved and is capable of supporting distinctly elevated testosterone levels. Although nutritional constraints likely underlie divergent patterns of testosterone secretion between Westernized and non-Western men, considerable variability exists in men's testosterone levels and prostate cancer rates within Westernized populations. Here, I use evolutionary life history theory as a framework to examine prostate cancer risk. Life history theory posits trade-offs between investment in early reproduction and long-term survival. One corollary of life history theory is the 'challenge hypothesis', which predicts that males augment testosterone levels in response to intrasexual competition occurring within reproductive contexts. Understanding men's evolved steroid physiology may contribute toward understanding susceptibility to prostate cancer. Among well-nourished populations of Westerners, men's testosterone levels already represent an outlier of cross-cultural variation. I hypothesize that Westernized men in aggressive social environments, characterized by intense male-male competition, will further augment testosterone production aggravating prostate cancer risk.

Cancer morbidity of professional emergency responders in Korea

BACKGROUND

Many professional emergency responders (ERs) who belong to the Korean National Emergency Management Agency (NEMA) have been cross-trained and serve multiple roles. As such, firefighters and other ERs in Korea are exposed to similar occupational hazards. This study was conducted to estimate cancer morbidity in male ERs and compare that with Korean men.

METHODS

The cohort was comprised of 33,416 male ERs working between 1980 and 2007, who were alive on December 31, 1995. Work histories were merged with the Korea National Central Cancer Registry (KNCCR) to assess cancer morbidity between 1996 and 2007. Standardized incidence ratios (SIRs) with reference to Korean men were analyzed.

RESULTS

SIRs with reference to national cancer rates were not significantly decreased for overall cancer (SIR = 0.97, 95% CI = 0.90-1.08) in all ERs. However, colorectal (SIR = 1.35, 95% CI = 1.07-1.67), kidney (SIR = 1.59, 95% CI = 1.00-2.41), and bladder (SIR = 1.77, 95% CI = 1.08-2.73) cancer, and non-Hodgkin's lymphoma (SIR = 1.81, 95% CI = 1.12-2.76) morbidities were significantly increased among all ERs. In firefighters, significantly increased cancer types were as same as those of all ERs. In non-firefighter ERs, colorectal (SIR = 2.51, 95% CI = 1.20-4.61) and bone and articular cartilage cancers (SIR = 9.53, 95% CI = 1.07-34.41) were significantly higher than those of Korean men.

CONCLUSIONS

Korean firefighters showed excess morbidity in several cancer types, including colorectal and urologic cancers, and non-Hodgkin's lymphoma, demonstrating similar trends to previous studies for firefighters conducted in other countries. Increased incidence in these cancer types suggests occupational exposure to carcinogens and shift work.

Adolescent and adult risk factors for testicular cancer

The incidence of testicular cancer has been increasing over the past several decades in many developed countries. The reasons for the increases are unknown because the risk factors for the disease are poorly understood. Some research suggests that in utero exposures, or those in early childhood, are likely to be important in determining an individual's level of risk. However, other research suggests that exposure to various factors in adolescence and adulthood is also linked to the development of testicular cancer. Of these, two adult occupational exposures-fire fighting and aircraft maintenance--and one environmental exposure (to organochlorine pesticides) are likely to be associated with increased risk of developing testicular cancer. By contrast, seven of the identified factors--diet, types of physical activity, military service, police work as well as exposure to ionizing radiation, electricity and acrylamide--are unlikely to increase the risk of developing testicular cancer. Finally, seven further exposures--to heat, polyvinyl chloride, nonionizing radiation, heavy metals, agricultural work, pesticides and polychlorinated biphenyls as well as marijuana use--require further study to determine their association with testicular cancer.

Influence of the Circadian System on Disease Severity

The severity of many diseases varies across the day and night. For example, adverse cardiovascular incidents peak in the morning, asthma is often worse at night and temporal lobe epileptic seizures are most prevalent in the afternoon. These patterns may be due to the day/night rhythm in environment and behavior, and/or endogenous circadian rhythms in physiology. Furthermore, chronic misalignment between the endogenous circadian timing system and the behavioral cycles could be a cause of increased risk of diabetes, obesity, cardiovascular disease and certain cancers in shift workers. Here we describe the magnitude, relevance and potential biological basis of such daily changes in disease severity and of circadian/behavioral misalignment, and present how these insights may help in the development of appropriate chronotherapy.

Cancer incidence among male Massachusetts firefighters, 1987-2003

BACKGROUND

Firefighters are known to be exposed to recognized or probable carcinogens. Previous studies have found elevated risks of several types of cancers in firefighters.

METHODS

Standardized morbidity odds ratio (SMORs) were used to evaluate the cancer risk in white, male firefighters compared to police and all other occupations in the Massachusetts Cancer Registry from 1986 to 2003. Firefighters and police were identified by text search of the usual occupation field. All other occupations included cases with identifiable usual occupations not police or firefighter. Control cancers were those not associated with firefighters in previous studies.

RESULTS

Risks were moderately elevated among firefighters for colon cancer (SMOR = 1.36, 95% CI: 1.04-1.79), and brain cancer (SMOR = 1.90, 95% CI: 1.10-3.26). Weaker evidence of increased risk was observed for bladder cancer (SMOR = 1.22, 95% CI: 0.89-1.69), kidney cancer (SMOR = 1.34, 95% CI: 0.90-2.01), and Hodgkin's lymphoma (SMOR = 1.81, 95% CI: 0.72-4.53).

CONCLUSIONS

These findings are compatible with previous reports, adding to the evidence that firefighters are at increased risk of a number of types of cancer.

Occupational risk factors for prostate cancer

BACKGROUND

Occupational risk factors for prostate cancer have been investigated with inconsistent findings.

METHODS

This was a population-based case-control study of men in Northeastern Ontario, Canada. Cases (n = 760) were from the Ontario Cancer Registry, 50 to 84 years old, and diagnosed with prostate cancer between 1995 and 1998. Age-frequency matched controls (n = 1,632) were obtained from telephone listings. A questionnaire yielded information on occupational history and self-reported exposures to a list of occupational hazards. Exposures to these hazards were assessed by an occupational hygienist.

RESULTS

An odds ratio estimate (OR) of 1.21 (95 percent confidence interval (% CI) 1.01, 1.46) was found for employment in trades, transport and equipment operators and related occupations, possibly related to exposure to whole-body vibration (OR = 1.38, 95% CI 1.07, 1.78). For the highest quartile of lifetime cumulative workplace physical activity an OR of 1.33 (95% CI 1.02, 1.74) was found. No statistically significant associations were found for any other occupational category or exposure.

CONCLUSIONS

This study does not provide strong evidence for significant occupational risk factors for prostate cancer. However, whole-body vibration exposures, as well as physical activity, may be worth pursuing in future occupational studies.

Registry-based case-control study of cancer in California firefighters

BACKGROUND

There is no consensus whether firefighters are at increased cancer risk for particular cancers. Previous studies have been small, mostly investigated cancer mortality, and suggested increased risks for brain, bladder, testicular, prostate, thyroid and colo-rectal cancers, leukemia, and melanoma.

METHODS

Records of all male cancers registered in California during 1988-2003 were obtained. Firefighters were identified from occupation and industry text fields. Logistic regression analysis used other cancers as controls.

RESULTS

Of the 804,000 eligible records, 3,659 had firefighting as their occupation. Firefighting was associated with testicular cancer (odds ratio = 1.54, 95% confidence interval: 1.18-2.02), melanoma (1.50, 1.33-1.70), brain cancer (1.35, 1.06-1.72), esophageal cancer (1.48, 1.14-1.91), and prostate cancer (1.22, 1.12-1.33).

CONCLUSIONS

Use of other-cancer controls and lack of an occupational history may have biased relative risks towards the null. However, this study, which contained more firefighter cancers than any previous epidemiologic study, produced evidence supporting some prior hypotheses.

Cancer risk among firefighters: a review and meta-analysis of 32 studies

OBJECTIVE

The objective of this study was to review 32 studies on firefighters and to quantitatively and qualitatively determine the cancer risk using a meta-analysis.

METHODS

A comprehensive search of computerized databases and bibliographies from identified articles was performed. Three criteria used to assess the probable, possible, or unlikely risk for 21 cancers included pattern of meta-relative risks, study type, and heterogeneity testing.

RESULTS

The findings indicated that firefighters had a probable cancer risk for multiple myeloma with a summary risk estimate (SRE) of 1.53 and 95% confidence interval (CI) of 1.21-1.94, non-Hodgkin lymphoma (SRE = 1.51, 95% CI = 1.31-1.73), and prostate (SRE = 1.28; 95% CI = 1.15-1.43). Testicular cancer was upgraded to probable because it had the highest summary risk estimate (SRE = 2.02; 95% CI = 1.30-3.13). Eight additional cancers were listed as having a "possible" association with firefighting.

CONCLUSIONS

Our results confirm previous findings of an elevated metarelative risk for multiple myeloma among firefighters. In addition, a probable association with non-Hodgkin lymphoma, prostate, and testicular cancer was demonstrated.

Cancer incidence in Florida professional firefighters, 1981 to 1999

OBJECTIVE

The objective of this study was to examine the cancer risk associated with firefighting.

METHODS

Standardized incidence ratio analysis (SIR) was used to determine the relative cancer risk for firefighters as compared with the Florida general population.

RESULTS

Among 34,796 male (413,022 person-years) and 2,017 female (18,843 person-years) firefighters, 970 male and 52 female cases of cancer were identified. Male firefighters had significantly increased incidence rates of bladder (SIR = 1.29; 95% confidence interval = 1.01-1.62), testicular (1.60; 1.20-2.09), and thyroid cancers (1.77; 1.08-2.73). Female firefighters had significantly increased incidence rates of overall cancer (1.63; 1.22-2.14), cervical (5.24; 2.93-8.65), and thyroid cancer (3.97; 1.45-8.65) and Hodgkin disease (6.25; 1.26-18.26).

CONCLUSIONS

Firefighting may be associated with an increased risk of selected site-specific cancers in males and females, including an overall increased cancer risk in female firefighters.

Circadian Disruption, Shift Work and the Risk of Cancer: A Summary of the Evidence and Studies in Seattle

There is increasing interest in the possibility that disruption of normal circadian rhythm may increase the risk of developing cancer. Persons who engage in nightshift work may exhibit altered nighttime melatonin levels and reproductive hormone profiles that could increase the risk of hormone-related diseases, including breast cancer. Epidemiologic studies are now beginning to emerge suggesting that women who work at night, and who experience sleep deprivation, circadian disruption, and exposure to light-at-night are at an increased risk of breast cancer, and possibly colorectal cancer as well. Several studies have been conducted in Seattle recently to investigate the effects of factors that can disrupt circadian rhythm and alter normal nocturnal production of melatonin and reproductive hormones of relevance to breast cancer etiology. Studies completed to date have found: (1) an increased risk of breast cancer associated with indicators of exposure to light-at-night and night shift work; and (2) decreased nocturnal urinary levels of 6-sulphatoxymelatonin associated with exposure to 60-Hz magnetic fields in the bedroom the same night, and a number of other factors including hours of daylight, season, alcohol consumption and body mass index. Recently completed is an experimental crossover study designed to investigate whether exposure to a 60-Hz magnetic field under controlled conditions in the home sleeping environment is associated with a decrease in nocturnal urinary concentration of 6-sulphatoxymelatonin, and an increase in the urinary concentration of luteinizing hormone, follicle stimulating hormone, and estradiol in a sample of healthy women of reproductive age. Presently underway is a study to determine whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased urinary concentrations of the reproductive hormones listed above in a sample of healthy women of reproductive age, and to elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified. A proposal is under review to extend these studies to a sample of healthy men to investigate whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased concentrations of urinary cortisol and cortisone, urinary levels of a number of androgen metabolites, and serum concentrations of a number of reproductive hormones. Secondarily, the proposed study will elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified, as well as investigate whether polymorphisms of the genes thought to regulate the human circadian clock are associated with the ability to adapt to night shift work. It is anticipated that collectively these studies will enhance our understanding of the role of circadian disruption in the etiology of cancer.

The influence of occupational exposure to pesticides, polycyclic aromatic hydrocarbons, diesel exhaust, metal dust, metal fumes, and mineral oil on prostate cancer: a prospective cohort study

AIMS

To investigate the relation between exposure to pesticides, polycyclic aromatic hydrocarbons (PAHs), diesel exhaust, metal dust, metal fumes, and mineral oil in relation to prostate cancer incidence in a large prospective study.

METHODS

This cohort study was conducted among 58,279 men in the Netherlands. In September 1986, cohort members (55-69 years) completed a self-administered questionnaire on potential cancer risk factors, including job history. Follow up for prostate cancer incidence was established by linkage to cancer registries until December 1995 (9.3 years of follow up). The analyses included 1386 cases of prostate cancer and 2335 subcohort members. A blinded case-by-case expert exposure assessment was carried out to assign cases and subcohort members a cumulative probability of exposure for each potential carcinogenic exposure.

RESULTS

In multivariate analyses there was a significant negative association for pesticides (RR 0.60; 95% CI 0.37 to 0.95) when comparing the highest tertile of exposure to pesticides with no exposure. No association was found for occupational exposure to PAHs (RR 0.75; 95% CI 0.42 to 1.31), diesel exhaust (RR 0.81; 95% CI 0.62 to 1.06), metal dust (RR 1.01; 95% CI 0.72 to 1.40), metal fumes (RR 1.11; 95% CI 0.80 to 1.54), or mineral oil (RR 0.99; 95% CI 0.66 to 1.48) when comparing the highest tertile of exposure with no exposure. In subgroup analysis, with respect to tumour invasiveness and morphology, null results were found for occupational exposure to pesticides, PAH, diesel exhaust, metal dust, metal fumes, and mineral oil.

CONCLUSIONS

These results suggest a negative association between occupational exposure to pesticides and prostate cancer. For other carcinogenic exposures results suggest no association between occupational exposure to PAHs, diesel exhaust, metal dust, metal fumes, or mineral oil and prostate cancer.

A case?control study of occupational risk factors for bladder cancer in Canada

OBJECTIVE

To investigate occupational risk factors for bladder cancer in seven Canadian provinces.

METHODS

We analysed a population-based case-control dataset of 887 individuals with incident, histologically confirmed bladder cancer between 1994 and 1997. Controls (2847) frequency matched for age and gender were surveyed in 1996. Questionnaires were returned by about 60% of subjects. Odds ratios (ORs) for occupations and self-reported exposures were adjusted for province, age, race, smoking, and several dietary factors, using unconditional logistic regression.

RESULTS

Statistically significant increased risks were observed among men employed as hairdressers (OR = 3.42; 1.09-10.8), primary metal workers (OR = 2.40; 1.29-4.50), miners (OR = 1.94; 1.18-3.17), and automechanics (OR = 1.69; 1.02-2.82). Primary metal workers and automechanics showed evidence of an employment duration-response trend. Modest elevated risks that were not significant were also observed for male government inspectors, printers, firefighters, general labourers, and welders. A duration-response trend was evident for government inspectors and general labourers. For females, significant elevations were observed among lumber processors (OR = 8.78; 1.28-60.1), general labourers (OR = 2.18; 1.05-4.52), nurses (OR = 1.54; 1.03-2.31), and general clerks (OR = 1.48; 1.01-2.17). The latter showed a positive duration-response trend.

CONCLUSIONS

This study found a statistically significant excess risk of bladder cancer, with a duration-response trend, among male primary metal workers and automechanics, and female office workers engaged in general clerical duties.

Intracranial Neoplasms

This chapter begins with a discussion of the taxonomy of primary brain tumors, with a focus on gliomas, meningiomas, and grading systems for these tumors. It discusses methodological challenges for studies of brain tumor incidence including variations in diagnostic practices. It summarizes descriptive epidemiology studies of brain tumor incidence and mortality by age, sex, histologic type, and ethnicity. Factors associated with survival are discussed including histologic grade, tumor location, and extent of surgical resection. Much work remains to discover the causes of the majority of human brain tumors, as established risk factors account for only a small proportion of these tumors. The chapter critiques evidence regarding possible risk factors for brain tumors, including genetic predisposition, ionizing radiation, chemical carcinogen exposure, electromagnetic fields, infections, head trauma, smoking, and diet.

Serum pneumoproteins: a cross-sectional comparison of firefighters and police

BACKGROUND

Serum pneumoproteins provide a measure of the permeability of the lower respiratory tract, and have shown promise as a biomarker of acute and chronic exposure to respiratory toxicants.

METHODS

To evaluate the effects of chronic occupational smoke exposure, 105 firefighters were compared with 44 police controls in a cross-sectional study using spirometry, diffusing capacity of the lung, serum Clara cell protein (CC16), and serum surfactant-associated protein A (SP-A) measurements.

RESULTS

There were no significant differences in age, gender, height, spirometry (FVC and FEV(1)), and diffusing capacity between the two groups. Serum SP-A was lower in firefighters (260.1 +/- 121.2 microg/L) than police (316.0 +/- 151.4 microg/L, P = 0.019). Serum CC16 was also lower in firefighters (8.39 +/- 3.11 microg/L) than police (10.56 +/- 4.20 microg/L, P < 0.001), although this difference lost statistical significance when adjusted for confounders.

CONCLUSIONS

Firefighters have lower serum concentrations of SP-A than do police. Although the clinical significance of this finding is presently unknown, SP-A deserves further study as a biomarker of toxic exposure to the lower respiratory tract.

Firefighting and risk of testicular cancer: results from a German population-based case-control study

BACKGROUND

There is some evidence of an elevated risk for testicular cancer among firefighters.

METHODS

We performed a population-based case-control study including 269 testicular cancer cases and 797 controls matching on age and region with a special focus on occupational exposures. Job tasks were coded according to the International Standard Classification of Occupations (ISCO 68). We used conditional logistic regression to calculate odds ratios (OR).

RESULTS

Three controls (0.4%) and four cases (1.5%) ever worked as firefighters. Firefighters showed an increased odds of testicular cancer in the matched evaluation (OR = 4.3, 95% confidence interval (95% CI) 0.7-30.5). The adjustment for a history of cryptorchidism or family history of testicular cancer did not alter our results.

CONCLUSION

Although the association between firefighting and testicular cancer risk is based on only small numbers of exposed subjects in our study, the finding is consistent with a recent cohort study from New Zealand. Occupational hazards experienced by firefighters may increase the risk of testicular cancer.

Is testicular cancer an occupational disease of fire fighters?

BACKGROUND

A previous investigation showed an increased risk of testicular cancer among fire fighters in Wellington City, New Zealand, during the 1980s. Other studies of fire fighters had not identified testicular cancer as an occupational disease.

METHODS

This was an historical cohort study of mortality and cancer incidence in all paid New Zealand fire fighters, from 1977 to 1995.

RESULTS

The only cancer for which this study provided evidence of an increased risk was testicular cancer, even after excluding cases from the previous investigation. The standardized incidence ratio for 1990-96 was 3.0 (95% confidence interval: 1.3-5.90). There was no evidence that fire fighters were at increased risk from any particular cause of death.

CONCLUSIONS

This study confirmed that New Zealand fire fighters are at increased risk of testicular cancer, although the reason is unknown. Other incidence studies of cancer in fire fighters are needed to confirm this finding.

Cohort mortality study of Philadelphia firefighters

BACKGROUND

Fire fighters are exposed to a wide variety of toxic chemicals. Previous studies have reported excess risk of some cancers but have been limited by small numbers or little information on employment characteristics.

METHODS

We conducted a retrospective cohort mortality study among 7,789 Philadelphia firefighters employed between 1925 and 1986. For each cause of death, the standardized mortality ratios (SMRs) and 95% confidence intervals were estimated. We also compared mortality among groups of firefighters defined by the estimated number of career runs and potential for diesel exposure.

RESULTS

In comparison with U.S. white men, the firefighters had similar mortality from all causes of death combined (SMR = 0.96) and all cancers (SMR = 1.10). There were statistically significant deficits of deaths from nervous system diseases (SMR = 0.47), cerebrovascular diseases (SMR = 0.83), respiratory diseases (SMR = 0.67), genitourinary diseases (SMR = 0.54), all accidents (SMR = 0.72), and suicide (SMR = 0.66). Statistically significant excess risks were observed for colon cancer (SMR = 1.51) and ischemic heart disease (SMR = 1.09). The risks of mortality from colon cancer (SMR = 1.68), kidney cancer (SMR = 2.20), non-Hodgkin's lymphoma (SMR = 1.72), multiple myeloma (SMR = 2.31), and benign neoplasms (SMR = 2.54) were increased among firefighters with at least 20 years of service.

CONCLUSIONS

Our study found no significant increase in overall mortality among Philadelphia firefighters. However, we observed increased mortality for cancers of the colon and kidney, non-Hodgkin's lymphoma and multiple myeloma. There was insufficient follow-up since the introduction of diesel equipment to adequately assess risk.

Assessment of exposure to polycyclic aromatic hydrocarbons during firefighting by measurement of urinary 1-hydroxypyrene

Firefighters may be exposed to carcinogenic agents in the smoke from fires, and there has been some concern regarding firefighters' risk of developing occupational-related cancer. Polycyclic aromatic hydrocarbons (PAHs) are present in most fires, posing a cancer risk. The objective of this study was to evaluate the PAH exposure among firefighters. Students (n = 9) and teachers (n = 4) at a firefighter training school delivered urine samples before and 6 to 7 hours after extinguishing burning diesel fuel. The urine samples were analyzed by high-performance liquid chromatography for 1-hydroxypyrene. A small but significant increase in 1-hydroxypyrene levels in the urine was found after the firefighting. This means that firefighting may cause exposure to PAHs. Although the exposure levels were low in this study, they may be different during other types of fires.