Historical cohort study of US man-made vitreous fiber production workers: IV. Quantitative exposure-response analysis of the nested case-control study of respiratory system cancer

As part of the 1992 update of an historical cohort study of 32,110 workers employed for at least 1 year in any of 10 US fiberglass manufacturing plant s, a nested case-control study was done in which data on tobacco smoking we re obtained for 631 male case subjects with respiratory system cancer (RSC) and 570 control subjects matched on age and year of birth. In this more ex tensive analysis of the nested case-control data, we provide a detailed ass essment of the most prominent findings from the initial report. We expand t he scope of the analysis to consider quantitative measures of exposure to r espirable fibers (RFib), formaldehyde (FOR), and silica (Sil) and consider these and other exposures together in the same model. We investigate the fu nctional form of possible exposure-response relationships between RSC risk, PLFib, and FOR. In addition, we address the statistical issues of collinea rity, effect modification, and potential confounding by coexposures. All an alyses are adjusted for smoking. Neither measure of exposure to RFib (avera ge intensity of exposure or cumulative exposure) was statistically signific antly associated with RSC risk in any of the hundreds of fractional polynom ial models considered. This more extensive analysis has substantiated our i nitial finding of no apparent exposure-response relationship between RSC ri sk and either cumulative or average intensity of exposure to PLFib at the l evels experienced by these workers. This study provides some evidence of in creased RSC risk among workers at the higher observed levels of average int ensity of exposure to FOR and/or Sil. No positive associations were identif ied between RSC risk and any of the other exposures considered in this case -control study.