Case‐control study of silicosis, silica exposure, and lung cancer in white South African gold miners

Abstract

A case‐control study was undertaken to assess the association between lung cancer and silicosis or silica dust exposure in white South African gold miners. Cases and controls were identified from deaths reported to the Gold Miners Provident Fund for the period January, 1979–October, 1983. Two controls were matched to each case by year of birth (± 2 years) and by smoking (± 5 cigarettes or equivalents per day) assessed 10 years (± 2 years) prior to death. One hundred thirty‐three matched triplets were identified. The results showed no overall association between lung cancer and radiological silicosis (OR = 1.08, p = 0.92). Autopsy data indicated no overall associations between lung cancer and silicosis of the lung parenchyma (OR = 1.49, p = 0.11), the pleura (OR = 0.72, p = 0.30), or the hilar glands (OR = 0.85, p = 0.72). A trend toward increased severity of silicosis of the parenchyma was evident; however, this was not statistically significant (p = 0.08). Odds ratios for lung cancer and silicosis were higher at lower levels of cumulative silica dust exposure (ORs = 2.43, 1.72, 1.35 and 0.62 for lung cancer and autopsy silicosis of the parenchyma for the lowest, second, third, and highest quartiles of dust exposure, respectively; all p > 0.05). Cases did not differ from controls for total silica dust exposure, length of exposure, weighted average intensity of exposure, or number of shifts at high dust (all p > 0.20). The data do not support the hypothesis of a carcinogenic role for silica dust and no statistically significant associations were found between lung cancer and silicosis. Trends in the data on the severity of parenchymal silicosis at autopsy and lung cancer and differences in the association between silicosis and lung cancer at various levels of dust exposure are suggestive and warrant further study.