LETTERS: Letters to the Editor
The author responds:
Erren and his coauthors1 agree that there is sufficient evidence to conclude that “exposure to silica is causally associated with an increased risk of lung cancer.” However, they add that there is still a “critical ‘but,’” which is whether silicosis is required for silica-associated lung cancer. I agree with the authors that this is indeed an important unresolved question, which has large medico-legal and regulatory implications. If silicosis were necessary for silica-induced lung cancer, then a case of lung cancer without silicosis might be dismissed as being unrelated to silica. If occupational standards for silica are set at a level that would prevent silicosis, then this would also eliminate excess lung cancer. This is somewhat moot given that the OSHA standard for silica is associated with a substantial risk of silicosis2–4 as well as lung cancer.5,6 The question has greater relevance for environmental exposures, which are generally below levels where silicosis has been reported to occur. If their conjecture is true, this may suggest that there is a threshold for silicosis and hence for lung cancer. However, the absence of evidence of silicosis for environmental exposures does not necessarily imply a threshold, and might be explained by limitations of the diagnostic tests or low power of studies to detect weak effects.
Most studies have not found an association between silica and lung cancer among individuals without silicosis,7–10 while some have.11 Interpretation of these mostly negative findings is complicated by the facts that silicosis may also be regarded as a marker of heavy exposure to silica and that the diagnosis of lung cancer may increase the likelihood of silicosis detection. Study results indicating an increase in lung cancer among persons without silicosis might be attributable to underascertainment of silicosis based on chest radiographs. Comparisons of findings from pathologic exams at autopsy with chest radiographs have shown that the use of chest radiographs may grossly underestimate the prevalence of silicosis.12
Finally, Erren et al1 suggest that further research is needed to resolve this important issue in order to be able to “make sound public health decisions concerning silica at the low end of the exposure scale.” In 2000 Checkoway and Franzblau13 suggested that the question of whether or not silicosis required for elevated lung cancer risk “is virtually unanswerable.” Unfortunately this situation has not improved since their review and is unlikely to change in the near future.
Division of Epidemiology and Biostatistics, University of Illinois, Chicago School of Public Health, Chicago, IL email@example.com
1. Erren TC, Morfeld P, Glende CB, et al. Silica and lung cancer [letter]. Epidemiology
2. Park R, Rice F, Stayner L, et al. Exposure to crystalline silica, silicosis and lung disease other than cancer in diatomaceous earth industry workers: a quantitative risk assessment. Occup Environ Med
3. ′t Mannetje A, Steenland K, Attfield M, et al. Exposure-response analysis and risk assessment for silica and silicosis mortality in a pooled analysis of six cohorts. Occup Environ Med.
4. Rice FL, Stayner LT. Assessment of silicosis risk for occupational exposure to crystalline silica. Scan J Work Environ Health
. 1995;21(Suppl 2):87–90.
5. Rice FL, Park R, Stayner L, et al. Crystalline silica exposure and lung cancer mortality in diatomaceous earth industry workers: a quantitative risk assessment. Occup Environ Med
6. Steenland K, Mannetje A, Boffetta P, et al. Pooled exposure-response analyses and risk assessment for lung cancer in 10 cohorts of silica-exposed workers: an IARC multicentre study. Cancer Causes Controls
7. de Klerk NH, Musk AW. Silica, compensated silicosis, and lung cancer in Western Australian goldminers. Occup Environ Med
8. Dong D, Xu G, Sun Y, et al. Lung cancer among workers exposed to silica dust in Chinese refractory plants. Scand J Work Environ Health
. 1995;21(Suppl 2):69–72.
9. Finkelstein MM. Radiographic abnormalities and the risk of lung cancer among workers exposed to silica dust in Ontario. Can Med Assoc J
10. Ulm K, Gerein P, Eigenthaler J, et al. Silica, silicosis and lung-cancer: results from a cohort study in the stone and quarry industry. Int Arch Occup Environ Health
11. Checkoway H, Hughes JM, Weill H, et al. Crystalline silica exposure, radiological silicosis, and lung cancer mortality in diatomaceous earth industry workers. Thorax
12. Hnizdo E, Murray J, Sluis-Cremer GK, et al. Correlation between radiological and pathological diagnosis of silicosis: an autopsy population based study. Am J Ind Med
13. Checkoway H, Franzblau A. Is silicosis required for silica-associated lung cancer. Am J Ind Med