PROGNOSIS OF COAL-MINERS WITH CANCER OF THE LUNG

Silica, pneumoconiosis, and carcinoma of the lung

The current argument about the carcinogenicity of inhaled silica is not clarified by reliance on morbidity and mortality experience divorced from or incompletely related to data on environmental exposure. Human evidence provides the ultimate basis for assessing such risks, and numerous studies of the effects of inhaling dusts rich or poor in silica content on the prevalence of pulmonary carcinoma have been performed on large series of cases from major mining areas of the world. When due allowance is made for substances inhaled concomitantly with exposure to silica and for personal pollution by cigarette smoking, the weight of evidence is against a carcinogenic role for uncombined silicon dioxide. Moreover, pneumoconiosis due to compact mineral particles does not appear to determine the onset of lung cancer. Cellular behaviour suggests reasons for the different responses to compact and fibrous particles acting alone.

Lung cancer in miners

The clinical, histological, and biological features of 157 lung cancers in coal miners and ex-miners are presented. In most respects—age, bronchoscopic appearances, histological type, and symptoms —the two groups are similar. A high incidence of dyspnoea in the miners was attributed to the concurrence of chronic bronchopulmonary disease. A striking feature was the lower frequency with which lung cancer in miners was found to be operable. It was suggested that the lower frequency of lung cancer in miners is related to an enhancement of the state of immunological preparedness in the lung related to the immune component in the pathogenesis of pneumoconiosis. The differences in lung cancer between miners and non-miners may be partially explained in this way.