Association Between Job Characteristics, Benzene Exposure, and Hematopoietic Cancer Risk in Subway Maintenance Workers

The occurrence of multiple cases of hematopoietic cancers (HC) among subway train maintenance workers (MWs) at a municipally owned metro company prompted an investigation into their association with this maintenance work. We aimed to evaluate the occurrence of HC among MWs relative to the general population and examine the association between job characteristics, past benzene exposure, and HC risk. A cohort of 4,438 MWs was analyzed for the period 2005–2024. HC cases were identified through self-reporting and coworker reports obtained from a structured questionnaire survey. Diagnoses were confirmed via follow-up interviews. Respective benzene exposure was assessed using a job-exposure matrix (JEM) based on maintenance type and the historical use of thinners. Standardized incidence ratios were calculated to compare HC occurrence among MWs with that of the general population, and Cox proportional hazards ratio (HR) was employed to evaluate HC risk. A total of eleven HC cases were identified, including leukemia (n=4) and non-Hodgkin lymphoma (n=7). The HC incidence risk among MWs was not significantly elevated compared with the general population. MWs classified with “definite” past benzene exposure probability had a significantly higher risk of HC than those with “possible” exposure (HR = 3.58, 95% CI = 1.09–11.75 ). Although qualitative benzene exposure levels suggested a potential association with HCs (HR for “high” group = 3.09, 95% CI = 0.69–13.84 and HR for “moderate” = 2.22, 95% CI = 0.55-8.93 vs. “low”), the results were not statistically significant. Extended follow-up and additional case identification among MWs are required to clarify maintenance-specific associations with HC risk