Reevaluation of silicosis and lung cancer in North Carolina dusty trades workers

Abstract

We previously reported on the lung cancer mortality through 1983 of 760 males who were diagnosed with silicosis during 1930-1983 by the State of North Carolina's medical examination program for dusty trades workers. The lung cancer SMR (95% confidence interval) was 2.6 (1.8-3.6) among 655 white members of this group. In this paper, we report the results of a reanalysis of mortality among a subgroup for whom chest radiographs were currently available for rereading. Technically acceptable radiographs were available for 306 white males and were independently reclassified for pneumoconiosis by 3 "B" readers using the 1980 ILO Classification. Lung cancer SMRs were 1.7 (0.8-3.1) for the entire group of 306 white males, 2.5 (1.1-4.9) for 143 subjects reclassified as simple silicosis, and 1.0 (0.1-3.5) for 96 subjects whose radiographs were reclassified as ILO category 0. There were no lung cancer deaths among 67 subjects whose radiographs were reclassified as progressive massive fibrosis. Corresponding lung cancer SMRs for subjects who had never been employed in a job with exposure to known occupational carcinogens were 1.2 (0.2-4.4) for those reclassified as category 0, and 2.4 (1.0-5.0) for those reclassified as having simple silicosis. The age-adjusted lung cancer rate ratio among subjects with simple silicosis compared to those with category 0 was 1.5 (0.4-5.8). Our findings from this reanalysis, which effectively controls for misclassification of silicosis due to errors in radiograph interpretation by North Carolina program readers, offer additional evidence consistent with the hypothesis of an association between silicosis and lung cancer in this study group.

Silicosis and Smoking Strongly Increase Lung Cancer Risk in Silica-Exposed Workers

“…We also chose 16 studies (11 cohort 4,9,11,15,[26][27][28][29][30][31][32] and 5 case-control studies 19,[33][34][35][36] ) which stated a relationship between silicosis and lung cancer risk (Tables 3 and 4). In addition, we selected 8 studies which presented lung cancer risk in non-silicotic subjects exposed to silica as well as silicotic subjects 4,9,11,15,19,31,33,37) (Table 5). We evaluated the common lung cancer risks from silica exposure, silicosis and non-silicosis with exposure to silica from these studies by meta-analysis.…”

Summary of Notifiable Noninfectious Conditions and Disease Outbreaks: Surveillance for Silicosis — Michigan and New Jersey, 2003–2010

“…Chinese pottery workers 10. Cohorts of registered silicotics from North Carolina [Amandus et al 1991[Amandus et al ,1992 and Finland [Kurppa et al 1986;Partanen et al 1994] Although a few of these studies did not find a statistically significant association between occupational exposure to crystalline silica and lung cancer (Table 15), most of the studies did.…”

“…§ Information bias involves misclassification of study subjects by disease or exposure status [Checkoway et al 1989]. An example of disease (silicosis) misclassification occurred in a study of North Carolina dusty trades workers [Amandus et al 1991;Rice et al 1986]: a re-evaluation of the chest X-rays found that 104 of the 370 cases categorized as silicosis were actually International Labour Organization (ILO) category 0 (nonsilicotic) [Amandus et al 1992]. Sources of exposure assessment errors include instrument error, incorrect imputation of exposure when data are missing, and data extrapolation errors [Checkoway 1995].…”

“…Consistent findings of excess risk in different countries, industries, and time periods 4. Two studies that provided reasonable evidence for an unconfounded association (i.e., Amandus et al [1991Amandus et al [ , 1992Amandus et al [ , 1995 and Partanen et al [1994], an update of Kurppa et al [1986])…”

“…C the presence of radiographically defined silicosis [Amandus et al 1992;Dong et al1995], and C length of followup time from date of silicosis diagnosis [Partanen et al 1994] (see Table 15). …”