Silica, compensated silicosis, and lung cancer in Western Australian goldminers.

Abstract

Objectives-Silica has recently been reclassified as carcinogenic to humans based largely on the observed increase in rates of lung cancer in subjects with silicosis. Other recent reviews have arrived at diVerent conclusions as to whether silicosis or silica itself is carcinogenic. This study aims to examine exposure-response relations between exposure to silica and subsequent silicosis and lung cancer in a cohort of goldminers. Methods-2297 goldminers from Kalgoorlie in Western Australia were examined in 1961, 1974, and 1975. Data were collected on respiratory symptoms, smoking habits, and employment history. Subjects were followed up to the end of 1993. Survival analyses for lung cancer mortality and incidence of compensated silicosis were performed with age and year matched conditional logistic regression analyses. Results-89% of the cohort were traced to the end of 1993. 84% of the men had smoked at some time and 66% were current smokers. 1386 deaths occurred during the follow up period, 138 from lung cancer, and 631 subjects were compensated for silicosis. A strong eVect of smoking on mortality from lung cancer, and a smaller eVect on the incidence of compensated silicosis was found. There was a strong eVect of duration and intensity of exposure on the incidence of silicosis. The risk of mortality from lung cancer increased after compensation for silicosis. Of all direct measures of exposure to silica, only log cumulative exposure was significantly related to incidence of lung cancer, but this eVect disappeared once the onset of silicosis was taken into account. Conclusions-The incidence of silicosis was clearly related to exposure to silica and the onset of silicosis conferred a significant increase in risk for subsequent lung cancer, but there was no evidence that exposure to silica caused lung cancer in the absence of silicosis. (Occup Environ Med 1998;55:243-248)

340 Cancer incidence and mortality among underground and surface gold miners in Western Australia

“…The finding of an increased risk of lung cancer among minersin particular underground miners-supports previous findings in this cohort (De Klerk et al, 1995;De Klerk and Musk, 1998). Increased risks of lung cancer in relation to duration of underground hard rock mining have also been described in other cohorts.…”

“…The SMR for prostate cancer pointed towards a lower risk for underground miners, but the incidence data showed a significantly increased incidence among underground miners. The overall increased mortality in the goldminers' cohort is, besides cancers, mainly attributable to pneumoconiosis (SMR ¼ 11.2, 95% CI 8.4-14.8) (De Klerk and Musk, 1998). The increased mortality from cancer among miners appeared to be mainly driven by lung cancer, as the SMR for any cancer dropped to 1.10 (95% CI 0.98-1.24) when lung cancer was excluded (data not shown).…”

“…Updated smoking details were obtained from 250 subjects via an additional questionnaire in 2000. Full employment details were recorded on miners' health record cards (De Klerk and Musk, 1998). Miners were required to have annual chest X-rays as long as they were employed as miners.…”

Meta-analysis of silicosis and lung cancer

“…Some data suggest that the progression of silicosis may be determined by total accumulated silica dust exposure (65). If silica was a true carcinogen, our finding would rather be interpreted as an indication of the dose-response relationship between silica exposure and lung cancer (66). Such a distinction is, however, irrelevant for compensatory boards in their assessment of patients with silicosis and lung cancer.…”

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

“…As a result, we chose 30 studies in 25 papers which stated a relationship between silica exposure and lung cancer risk: 17 cohort studies in 17 papers [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] (Table 1) and 13 case-control studies in 8 papers 13,[19][20][21][22][23][24][25] (Table 2). 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).…”