Does fiber glass pose a respiratory system cancer risk in humans? Latest findings from the US cohort and nested case-control studies

We report findings to date from our 1992 follow-up of the US fiber glass (FG) worker cohort, which includes 32110 workers from 10 study plants. Key findings include: (i) in all but one study plant, a higher prevalence of 'ever' cigarette smoking among male FG workers compared to the US and respective state populations; (ii) cigarette smoking strongly predicts respiratory system cancer (RSC) risk, strongly confounds the comparison of RSC risk between FG workers and the general population, and weakly confounds the exposure-response relationship between respirable fiber (RFib) and RSC; (iii) an overall 7% local county rate-based mortality excess for RSC among male workers appears to be entirely explained by positive confounding by smoking; (iv) the overall risk of mesothelioma does not appear to be elevated; (v) RSC risk does not increase with increasing levels of the categorical (weighted or unweighted) or quantitative (unweighted) RFib exposure measures considered; and (vi) with the possible exception of formaldehyde and silica, no positive associations were identified between RSC risk and any of the other co-exposures considered. Our findings to date from external comparisons in the cohort study and internal comparisons in the case-control study suggest that exposure to RFib at the levels encountered in the study plants is not associated with an increased risk of RSC or mesothelioma. These findings are generally similar to our previous 1985 follow-up of the original FG cohort, and to those other cohort studies of FG production workers conducted in the US, Canada and Europe. Ongoing or planned analyses include plant-specific analyses and will consider small diameter, special-application glass fibers and possibly more sensitive measuresof fiber exposure that account for such features as biopersistence and solubility.