Background: Some epidemiological studies have reported elevated risk of cancer mortality, most notably lymphohematopoietic cancers, among styrene-exposed workers.

Objective: We aimed to evaluate whether a cohort of workers exposed to styrene between 1948 and 1977 across 30 U.S. reinforced plastics facilities experienced elevated risk of cancer mortality compared to the U.S. national population.

Methods: We performed a mortality update of a historical cohort of 15,826-workers with follow-up occurring from 1948 through 2019 (extended from 2008). Standardized mortality ratios (SMRs) and 95% confidence intervals were computed by comparing observed deaths to expected deaths based on U.S. national-level age-, race-, sex-, and time-specific rates. Exposure-response trends were examined based on cumulative styrene exposure (ppm-months). Additional comparisons incorporating a 10-year lag and a 15-year latency period were performed.

Results: This update added 104,648 person-years of observation and 2,604 deaths. No statistically significant elevations in lymphohematopoietic cancer mortality were observed. Statistically significant excesses in mortality due to respiratory system cancer (SMR=1.30; 95% CI=1.22-1.39), cancer of the bronchus, trachea, and lung (SMR=1.31; 95% CI=1.22-1.40) and bronchitis, emphysema, and asthma (SMR=1.36; 95% CI=1.23-1.49) were observed. No statistically significant exposure-response trends were identified. Lag analyses and statistical comparisons accounting for latency yielded consistent results.

Conclusion: This cohort of U.S. reinforced plastics and composite industry workers experienced higher rates of mortality due to smoking-associated causes compared to the general U.S. population. Exposure-response analyses suggest these elevations may not be associated with styrene exposure. Analyses to evaluate the potential confounding effects of cigarette smoking in this cohort are planned.