Silica, Silicosis, and Lung Cancer: A Response to a Recent Working Group Report

Abstract

The relationship between crystalline silica and lung cancer has been the subject of many recent publications, conferences, and regulatory considerations. An influential, international body has determined that there was sufficient evidence to conclude that quartz and cristobalite are carcinogenic in humans. The present authors believe that the results of these studies are inconsistent and, when positive, only weakly positive. Other, methodologically strong, negative studies have not been considered, and several studies viewed as providing evidence supporting the carcinogenicity of silica have significant methodological weaknesses. Silica is not directly genotoxic and is a pulmonary carcinogen only in the rat, a species that seems to be inappropriate for assessing particulate carcinogenesis in humans. Data on humans demonstrate a lack of association between lung cancer and exposure to crystalline silica. Exposure-response relationships have generally not been found. Studies in which silicotic patients were not identified from compensation registries and in which enumeration was complete did not support a causal association between silicosis and lung cancer, which further argues against the carcinogenicity of crystalline silica.

Occupational Exposure to Silica and Lung Cancer: Pooled Analysis of Two Case-Control Studies in Montreal, Canada

“…Silica can cause chromosomal aberrations and transformation in vitro in mammalian cells (36). It has been found to be carcinogenic in rats, but not mice, guinea pigs, or hamsters (37). Endocytosis of single silica nanoparticles into human lung cancer cells has been seen on microscopy (38).…”

Mortality due to Silico-Tuberculosis and Lung Cancer Among 200 Whetstone Cutters.

“…Possible association of lung cancer with silicosis is a current focus of both medical and social attention. Whereas a significant increase in lung cancer mortality was not detected in never-smoking silicotics in some studies 19) , and the absence of association between lung cancer and exposure to crystalline silica was debated 20) , International Agency for Research on Cancer 2) , Japan Society for Occupational Health 3) and Committee on Pneumoconiosis and Lung Cancer 4) all concluded in the favor of positive association between silica exposure and cancer of the lungs, in agreement with the observations by various authors such as Forastiere et al 21) , Hnizdo and Sluis-Cremer 22) , Amandus et al 23) , Merlo et al 24) , Hughes et al 14) , and Steenland and Sanderson 25) . With regard to reports from Japan, Morinaga et al 16) observed an elevated relative risk for lung cancer of 3.7 among compensated silicotics; although the effects of smoking habits on the cancer incidence were not clear, they estimated that the elevation was too high to be attributed to smoking habits alone.…”

A Patient with Asbestos-Induced Lung Cancer Complicated by Silicosis.

“…On the other hand, the International Agency for Research on Cancer (IARC) recently classified crystalline silica as a human carcinogen 2) . However, no definite international consensus has been obtained concerning about the carcinogenesis due to silica 3) . We 4,5) previously reported a high incidence of lung cancer due to asbestos exposure among shipbuilding workers.…”