Project title: Estimating a standardized incidence ratio (SIR) for malignant melanoma cases diagnosed from 2000-2017 among career firefighters in the state of Washington
Completed in: 2021 | Faculty advisor: June T. Spector
Objective: Firefighters are exposed to occupational hazards including carcinogens working in states like Washington with laws that provide line-of-duty benefits for certain cancers; however, research on exposure-disease relationships is inconsistent for covered cancers like malignant melanoma (MM). The goal of this study was to characterize MM among career firefighters (FF) in Washington by: (1) identifying and describing MM cases diagnosed from 2000-2017 in career FF across multiple state counties, and (2) calculating a standardized incidence ratio (SIR) with 95% confidence interval using a standard population based on local, county-level estimations and an indirect standardization approach.
Methods: Linkage between the Cancer Surveillance System (CSS) and Law Enforcement Officers’ and Firefighters’ (LEOFF) Retirement System identified MM cases in the study population of career FF. The standard population with age-specific MM rates were calculated using annual observations per estimated population informed by the Washington State Cancer Registry (WSCR) restricted to the CSS 13-County region to adjust for age and the Multicounty 6 Region Scheme to adjust for age and sex. Total FF population and age distributions were furnished by the Office of the State Actuary. For the analysis, data were restricted to either a first or second primary melanoma diagnosis. Indirect standardization using age-specific MM rates in the standard population adjusted for age alone and adjusted for both age and sex was performed separately to estimate expected counts.
Results: A total of 184 observed MM cases with 16 (8.7%) cases among women and 168 (91.3%) among men were identified with almost all cases—182 (98.9%)—occurring in white firefighters. Many cases—102 (55.4%)—were reported from either an all-urban or mostly urban environment and 103 (56.0%) were diagnosed after retirement from firefighting. The most common area affected was the skin of the trunk in 64 (35%) cases. Eighty-five (46.2%) were classified as non-invasive (i.e., in-situ or stage 0 disease). Of the 95 invasive cases, the majority—66 (69.5%)—were Stage I, or in SEER Summary Stage parlance, 84 (88.4%) were considered early-stage disease. The estimated SIR for MM in career FF was 1.28 [95% CI 1.09, 1.46] after age adjustment only and 1.18 [95% CI 1.01, 1.35] after both age and male sex adjustment.
Conclusions: A diagnosis of melanoma is expected to occur in excess of 18% among career FF in the state of Washington when compared to the standard population used. Limitations of this study include suppressed age-specific rates by sex when counts were less than 10 to maintain privacy, unaccounted for calendar time at-risk, and another defined occupational group for comparison. Future research considerations might compare risks with other occupations already known to have an increased risk of MM (e.g., commercial airline crew and pilots) or where the MM risk is unknown, understudied, or simply assumed (e.g., outdoor workers).