This study investigated a bladder cancer cluster in a cohort of employees, predominately criminal investigators, participating in a medical surveillance program with the United States Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) between 1995 and 2007. Standardized incidence ratios (SIRs) were used to compare cancer incidences in the ATF population and the US reference population. Seven cases of bladder cancer (five cases verified by pathology report at time of analysis) were identified among a total employee population of 3,768 individuals. All cases were white males and criminal investigators. Six of seven cases were in the 30 to 49 age range at the time of diagnosis. The SIRs for white male criminal investigators undergoing examinations were 7.63 (95% confidence interval = 3.70–15.75) for reported cases and 5.45 (2.33–12.76) for verified cases. White male criminal investigators in the ATF population are at statistically significant increased risk for bladder cancer.
The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), a law enforcement agency within the United States Department of Justice, has been in the business of investigating the cause and origin of fires and explosions since the 1970s. ATF typically collaborates with other federal, state, and local authorities to provide this service through several venues. At the local level, criminal investigators with ATF, especially ones holding special designations as certified fire investigators (CFIs), work side-by-side with their state and local counterparts to assist with investigation of post-fire and post-blast scenes. These individuals may also serve on city-based federal arson task forces, in partnership with other federal, state, and local investigators, to address acute arson problems. At the national level, ATF maintains a well-trained national response team (NRT) which provides comprehensive response to assist these other jurisdictions with onsite investigation of major arson and bombing incidents. The NRT is a multispecialty team comprised of criminal investigators with post-fire and post-blast investigation expertise, explosives enforcement specialists, forensic chemists, fire protection engineers, and other technical experts. ATF established the NRT program in 1978 and subsequently instituted a program for certification of criminal investigators as fire investigators (CFIs) in 1986.
In 1995, ATF commenced a voluntary medical surveillance program for members of the NRT to monitor the health of participants working in the potentially hazardous environment of the post-fire/post-blast scene. The agency extended the voluntary program to all CFIs in 1997. By 2000, three white male participants of the program had reported diagnoses of bladder cancer between the years 1994 and 1999. All three individuals were nonsmokers and younger than 50 years of age when diagnosed. This information raised concern that a bladder cancer cluster was occurring among scene investigators. In response to this concern, in 2002 ATF mandated participation in the medical surveillance program for all NRT members, all explosives enforcement specialists, and all criminal investigators, including those not involved in post-fire/post-blast investigations. To facilitate future epidemiologic evaluation of the significance of the apparent cancer cluster, ATF also committed medical surveillance data entry into an electronic database. By 2006, four additional white male program participants had reported diagnoses of bladder cancer between 2001 and 2005. Combined, the seven reported cases ranged in age from 32 to 53 in the year of diagnosis. From a job title perspective, all cases were among criminal investigators, who comprised 96% of the employees participating in the surveillance program. In addition, six of the seven cases reported working post-fire and post-blast scenes while employed with ATF. None of the seven cases reported work histories which involved investigation of such scenes prior to their employment with ATF.
The presence of this cancer cluster generated two questions. First, was this group of employees, predominantly criminal investigators, experiencing a greater than expected incidence of bladder cancer from a demographic perspective? Second, was post-fire/post-blast scene investigation associated with increased risk for bladder cancer? Part 1 of this study addresses the question on cancer incidence and Part 2 addresses the question on cancer risk associated with investigation of these scenes. Analyses for both parts use data collected through the medical surveillance program.
In the United States, bladder cancer is expected to be the sixth most commonly occurring cancer, excluding basal and squamous cell skin cancers, in 2012 [
Recognized nondemographic risk factors include cigarette smoking, bladder birth defects, chronic bladder inflammation, genetic predisposition, use of herbal remedies containing aristolochic acid, drinking water containing arsenic and chlorination by-products, prior history of bladder cancer, chemotherapy and radiation therapy, and specific industries and occupations with exposures to known or suspect bladder carcinogens [
Smoking, the number one risk factor for bladder cancer, is estimated to cause approximately 50% of bladder cancer cases in men and 30% of cases in women [
As an occupation, the broad job category of law enforcement is generally not recognized for being at increased risk for bladder cancer. In 1987, Schulte et al. [
Part 1 of this study investigates the statistical significance of the incidence of bladder cancer in the ATF employee population comprised of criminal investigators and members of the NRT.
The time interval of this study is 1993, the year preceding diagnosis of the first bladder cancer case, through 2007. For this period, a full roster cohort was constructed from the annual staffing rosters provided by ATF for each calendar year from 1993 through 2007. The annual staffing rosters included all criminal investigators, explosives enforcement specialists, forensic chemists, fire protection engineers, and a small number of other specialists typically affiliated with NRT work, regardless of individual membership on the NRT or eligibility for participation in the medical surveillance program, who were currently working for ATF in each respective calendar year. ATF provided the demographic study parameters of gender, race, and age, and the job series and titles for all members of the full roster cohort. Members of the full roster cohort are dispersed throughout the United States and its territories Puerto Rico and Guam and may move around within this geographic area during their employment with ATF.
With the advent of the medical surveillance program in 1995, a subset of the full roster cohort, comprised of employees participating in the program, was created. As explained in the introduction, the program was initially voluntary and offered to members of the NRT, but became mandatory in 2002 for all criminal investigators, explosives enforcement specialists, and members of the NRT. Setup in partnership with Federal Occupational Health (FOH), United States Department of Health and Human Services, the program consisted of an annual evaluation which included a medical history and tobacco use questionnaire, physical examination, and laboratory and ancillary tests. Collection of detailed work history information, including job series and titles, began in 2003 with the institution of a work history questionnaire. The use of FOH’s electronic database, the Occupational Health Information Management System (OHIMS), to facilitate future epidemiologic evaluation of the bladder cancer cluster began in 2002. Data for key study variables from pre-2002 exams were retrospectively retrieved and also entered into OHIMS.
For the cohort of employees participating in the medical surveillance program from 1995 to 2007, pertinent data collected with each annual evaluation included the demographic variables, gender, race, and age, as well as cancer history and tobacco use history. Data on job series and titles were also provided by members of the cohort participating in the program between 2003 and 2007. The demographic data and the job series and titles data provided by ATF for the full roster cohort were subsequently cross-referenced with the same data provided by employees participating in the medical surveillance program. Any data inconsistencies between the two sources were resolved by medical record review or phone contact with employees.
As stated in the introduction, all bladder cancer cases were initially identified by employees self-reporting the diagnosis and year of diagnosis at the time of the annual medical surveillance evaluation. The self-reported cases were subsequently contacted by the occupational medicine physician overseeing the medical surveillance program, who informed them of the bladder cancer cluster and of the plans to evaluate the significance of the cluster through epidemiologic analysis and requested their assistance with voluntary provision of a pathology report for verification of case diagnosis. Requests for pathology reports were accompanied by provision of medical release forms for completion by cases.
This is a cohort study in which standardized incidence ratios (SIRs) were calculated for four defined populations of ATF employees to compare the observed bladder cancer case numbers in each ATF population with the expected cancer case numbers based on incidence rate in the US general population, appropriately adjusted for age and stratified by sex and race, as relevant to each of the four ATF populations. The US general population was chosen as the best reference population for analysis due to the nation-wide dispersion of ATF employees under study. As all the bladder cancer cases occurred among white male criminal investigators, the populations chosen for analysis included: (1) the full roster cohort comprising all males and females, (2) all white males in the full roster cohort, (3) all white males in the full roster cohort with examinations (cancer and tobacco use histories), and (4) all white males in the full roster cohort with both examinations and work histories who were also criminal investigators. Determination of the expected cancer incidence rate was based on data from the surveillance epidemiology and end results (SEER) program for the US population for the period 1993–2007. The SIR estimates the relative risk of bladder cancer incidence in the ATF population compared to the US population adjusted for age and stratified by race and gender. Computations for each population included determination of the person-year distribution during the study period, which served as the denominator for the respective SIR analysis. One person-year was counted for each year an individual was a member of the cohort. The person-years were arranged by five-year age increments and three five-year time intervals, 1993–1997, 1998–2002, and 2003–2007.
Table
Distribution of self-reported bladder cancers and employees in key ATF study populations by gender and race (1993–2007).
Study population | Males | Females | Total | Percent of full roster | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Whites | Nonwhites | Whites | Nonwhites | ||||||||
Cases | Employees (%) | Cases | Employees (%) | Cases | Employees (%) | Cases | Employees (%) | Cases | Employees (%) | ||
Full roster | 7 | 2723 (72.3%) | 0 | 570 (15.1%) | 0 | 358 (9.5%) | 0 | 117 (3.1%) | 7 | 3768 (100%) | 100.00 |
Examinations | 7 | 1885 (69.5%) | 0 | 467 (17.2%) | 0 | 271 (10.0%) | 0 | 89 (3.3%) | 7 | 2712 (100%) | 71.97 |
Examinations and work histories | 7 | 1771 (69.5%) | 0 | 441 (17.3%) | 0 | 253 (9.9%) | 0 | 84 (3.3%) | 7 | 2549 (100%) | 67.65 |
Criminal investigators with examinations and work histories | 7 | 1715 (69.2%) | 0 | 436 (17.6%) | 0 | 244 (9.8%) | 0 | 83 (3.4%) | 7 | 2478 (100%) | 65.76 |
The full roster cohort comprised 3,768 individuals (Table
Of the full roster cohort, 2,712 (72%) members participated in the medical surveillance program between 1995 and 2007 and had data for one or more examinations in the program’s electronic database (Table
Job history data, collected from employees between 2003 and 2007 at the time of the annual exam, were available for 2549 (68%) members of the full roster cohort. Of these individuals, 2478 (97%) were criminal investigators (Table
During the study period, seven individuals reported bladder cancer diagnoses. At the time of the analysis, five of the seven cases had provided medical documentation (pathology reports) verifying the diagnosis of bladder cancer and diagnosis year. Another case provided verifying documentation following the completion of the analysis.
As affirmed from review of pathology reports of the urinary bladder biopsies of the five cases verified at the time of the analysis, four of the cases were low grade papillary transitional cell carcinomas and one was transitional cell carcinoma
The first case was diagnosed in 1994 and the most recent case was diagnosed in 2005. As already known from the medical surveillance program, all bladder cancers occurred in white males and in criminal investigators. Table
Distribution of self-reported bladder cancer cases and of person-years observed for white males in full roster cohort by calendar period and age group.
Age group | 1993–1997 | 1998–2002 | 2003–2007 | Total | ||||
---|---|---|---|---|---|---|---|---|
Cases | Person-years | Cases | Person-years | Cases | Person-years | Cases | Person-years | |
0–4 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
5–9 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
10–14 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
15–19 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
20–24 | 0 | 25.1 | 0 | 81.6 | 0 | 71.3 | 0 | 178.0 |
25–29 | 0 | 642.9 | 0 | 611.6 | 0 | 749.7 | 0 | 2004.1 |
30–34 | 2 | 1730.8 | 0 | 1593.4 | 0 | 1670.6 | 2 | 4994.8 |
35–39 | 0 | 1321.5 | 0 | 2136.4 | 1 | 2125.1 | 1 | 5583.0 |
40–44 | 0 | 773.1 | 2 | 1329.7 | 0 | 2111.9 | 2 | 4214.6 |
45–49 | 0 | 1574.9 | 1 | 763.0 | 0 | 1291.9 | 1 | 3629.8 |
50–54 | 0 | 1046.2 | 1 | 1083.5 | 0 | 571.5 | 1 | 2701.1 |
55–59 | 0 | 261.6 | 0 | 383.1 | 0 | 264.5 | 0 | 909.2 |
60–64 | 0 | 12.4 | 0 | 113.1 | 0 | 95.9 | 0 | 221.4 |
65–69 | 0 | 3.9 | 0 | 5.7 | 0 | 43.3 | 0 | 52.9 |
70–74 | 0 | 1.8 | 0 | 2.7 | 0 | 3.0 | 0 | 7.5 |
75–79 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
80–84 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
85–89 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 |
| ||||||||
Total | 2 | 7394.0 | 4 | 8103.8 | 1 | 8998.7 | 7 | 24496.5 |
*The one remaining unverified cancer case occurred in the 1998–2002 time frame.
Table
Standardized incidence ratios (SIRs) of self-reported and verified urinary bladder cancer cases for the period 1993–2007.
Study population | Employee # | Person-years | Expected cases* | Observed cases | SIR | 95% CI | |
---|---|---|---|---|---|---|---|
Entire roster cohort | 3,768 | 34,818.01 | 2.91 | 7 | 2.41 | 1.17 | 4.96 |
Entire roster cohort** | 3,768 | 34,818.01 | 2.91 | 5 | 1.72 | 0.73 | 4.02 |
Roster white males | 2,723 | 24,496.47 | 2.39 | 7 | 2.93 | 1.42 | 6.07 |
Roster white males** | 2,723 | 24,496.47 | 2.39 | 5 | 2.09 | 0.90 | 1.91 |
Exam white males | 1,885 | 19,648.25 | 1.15 | 7 | 6.08 | 2.94 | 12.54 |
Exam white males** | 1,885 | 19,648.25 | 1.15 | 5 | 4.34 | 1.85 | 10.16 |
Job 1811 white males | 1,715 | 17,976.42 | 0.92 | 7 | 7.63 | 3.70 | 15.75 |
Job 1811 white males** | 1,715 | 17,976.42 | 0.92 | 5 | 5.45 | 2.33 | 12.76 |
*Expected number of cases calculated using US incidence rates from SEER for the same period.
**SIRs determined for the five verified cases with pathology reports.
Table
When computed with all seven cases, the SIR is 2.41 (95% CI 1.17–4.96) for the entire roster cohort, 2.93 (95% CI 1.42–6.07) for the white male cohort, 6.08 (95% CI 2.94–12.54) for white males with exams, and 7.63 (95% CI 3.70–15.75) for white male criminal investigators with exams and work histories (Table
Age-specific cancer incidence rates in the white male ATF population were greater than the rates for the adjusted U.S. reference SEER population for each age group in which cases occurred (Table
Age-specific white male bladder cancer incidence rates (1/100,000) for ATF and SEER (13 registries), with respective rate ratios, for the period 1993–2007.
Age | ATF | SEER | RR | 95% CI-L | 95% CI-U |
---|---|---|---|---|---|
20–24 | 0.00 | 0.37 | 0.00 | 0.00 | 0.00 |
25–29 | 0.00 | 0.57 | 0.00 | 0.00 | 0.00 |
30–34 | 40.04 | 1.17 | 34.32 | 3.78 | 124.24 |
35–39 | 17.91 | 2.80 | 6.40 | 0.19 | 35.63 |
40–44 | 47.45 | 5.83 | 8.13 | 0.89 | 29.45 |
45–49 | 27.55 | 13.13 | 2.10 | 0.06 | 11.68 |
50–54 | 37.02 | 25.33 | 1.46 | 0.04 | 8.14 |
55–59 | 0.00 | 50.57 | 0.00 | 0.00 | 0.00 |
60–64 | 0.00 | 88.33 | 0.00 | 0.00 | 0.00 |
65–69 | 0.00 | 145.70 | 0.00 | 0.00 | 0.00 |
70–74 | 0.00 | 209.43 | 0.00 | 0.00 | 0.00 |
75–79 | 0.00 | 275.40 | 0.00 | 0.00 | 0.00 |
80–84 | 0.00 | 327.83 | 0.00 | 0.00 | 0.00 |
85–89 | 0.00 | 353.73 | 0.00 | 0.00 | 0.00 |
Recognition of a bladder cancer cluster among white male criminal investigators participating in an ATF medical surveillance program raised concern that the employee population was experiencing a greater-than-expected incidence of bladder cancer and that post-fire/post-blast scene investigation might be associated with increased risk of bladder cancer. Part 1 of this epidemiologic study determined that bladder cancer incidence in the white male study population was significantly elevated statistically for the period 1993–2007.
This study illustrates the twofold utility of using a medical surveillance program to monitor the health of an employee population potentially exposed to hazardous agents and to perform epidemiologic analysis of the significance of cancer occurring within the population. Although the ATF medical surveillance program evolved over time in several ways, which included changing from voluntary to mandatory participation, and despite an annual participation rate of 50–67% after the program became mandatory, the requisite data were sufficient to perform SIRs for the ATF study population which showed white males to be at increased risk for bladder cancer when compared to white males in the US reference population.
All bladder cancer cases in the ATF cohort were reported by white males, who constituted about 72% of the full roster cohort. In the incidence analyses of the two larger ATF populations, the full roster cohort and white males in the full roster cohort, the cancer risk was elevated for analyses performed with both seven reported and five verified cases, but was only statistically significant for the analyses with the seven reported cases. Since these two ATF populations included individuals who had not participated in the medical surveillance program and whose cancer history was unknown, which amounted to 28% of the full roster cohort and 31% of white males in the full roster cohort, the actual number of cases of bladder cancer within these two populations could be greater than the observed seven reported and five verified cases, which would lead to even higher SIRs than the ones calculated with the seven and five cases. With the two smaller ATF populations, white males with exams and white male criminal investigators with exams, the computed SIRs were elevated and statistically significant with both seven reported and five verified cancer cases. The SIRs of the two smaller populations, understandably higher than those of the two larger populations, might best depict the true cancer risk for the ATF cohort as the reported cancer history is known for all individuals in these two smaller populations.
The finding that white male criminal investigators in the ATF population are at increased risk for bladder cancer is in contrast with the findings of prior epidemiologic studies of bladder cancer incidence in law enforcement occupations, in which law enforcement and related job categories were generally found not to be at increased risk for bladder cancer [
The magnitude of the SIRs computed in this study deserves some discussion. For the population of white male criminal investigators with exams, the SIRs were 7.63 (95% CI 3.70–15.75) for seven reported cases and 5.45 (95% CI 2.33–12.76) for five verified cases, and for the slightly larger population of all white males with exams, the SIRs were 6.08 (95% CI 2.94–12.54) for seven reported cases and 4.34 (95% CI 1.85–10.16) for five verified cases. In individual epidemiologic studies of bladder cancer incidence in other occupations and industries, statistically significant elevations in relative risk have been found with a 1.1-fold to fivefold increase [
The elevated risk for bladder cancer in the current study cohort also approximates the increased risk for bladder cancer seen in smokers compared to nonsmokers, as demonstrated in various epidemiologic studies which show smokers to have a twofold to sixfold increased risk for bladder cancer [
Although the elevated SIRs for the two populations with exams remained statistically significant when analyzed with only the five verified cases, having two of the seven reported cases (28%) unverified at the time of statistical analysis constitutes a weakness of the study and illustrates a limitation of using data from a medical surveillance program to conduct a cancer incidence analysis. With so few total cases, the difference in number between reported and verified cases can impact the significance of study outcomes, as demonstrated by comparing the SIRs computed with both the seven reported and the five verified cases for the full roster cohort and for white males in the full roster cohort. Since the study analysis was completed, ongoing effort to verify the unverified cases was successful in verifying one of the two cases.
Another point to make is that the SIRs on the populations with exams could in actuality be artificially high, as only 72% of individuals in the full roster cohort underwent physical examination and individuals without medical issues may have selectively avoided coming in for exams. Since the institution of the mandatory program in 2002, however, 86% of individuals employed by ATF between 2002 and 2007 obtained at least one exam during this time frame and these 2697 employees accounted for 99% of the 2712 individuals in the full roster cohort with exams. With this level of participation in the mandatory program since 2002, potential for bias due to exam avoidance is likely very limited.
In conclusion, white male members of the ATF cohort experienced statistically significant increased risk for bladder cancer when compared to white males in the US population for the study period 1993–2007. Among white males with exams and white male criminal investigators with exams, the elevated risk was demonstrated for computations with both seven reported and five verified cancer cases. There was no observed bladder cancer risk for nonwhite males and all females in the cohort study.
With six of the seven cases in the bladder cancer cluster, having known histories of investigating post-fire and post-blast scenes while employed with ATF, scene investigation work appeared to be linked with the observed increase in bladder cancer incidence. Part 2 of the study will evaluate the association of post-fire/post-blast scene work history and risk for bladder cancer, while controlling for tobacco use history.
The authors thank ATF for funding the epidemiologic study and paper preparation, FOH for providing support for the study, including but not limited to advocating for the medical surveillance program for ATF that discovered the reported bladder cancer cases, performing the examinations and ancillary tests on the employees participating in the program, and providing OHIMS for management of program data, and Bruce Higgins, database manager of OHIMS, for managing the database of the medical surveillance program and assisting with preparation of data for analysis. The opinions in this paper are the authors’ and do not necessarily represent the opinions of ATF or of FOH. S. R. Davis, X. Tao, E. J. Bernacki and A. S. Alfriend received funding for this study from the Bureau of Alcohol, Tobacco, Firearms and Explosives, Department of Justice, Washington, DC, USA.