Silicosis, mixed dust pneumoconiosis, and lung cancer.

A total of 764 autopsy cases with a pathological diagnosis of nonasbestos pneumoconiosis were investigated in a search for lung cancer: 146 patients bore 148 lung cancers (19.1%). The incidence of a lung cancer was associated positively with aging longer occupational exposures, and smoking habits. A reverse correlation was found between carcinogenesis and the severity of pneumoconiosis. A statistically significant increase in the incidence of certain types of lung cancer (squamous cell carcinoma + small cell carcinoma) was found in silicotic lungs with massive fibrosis as compared to lungs with mixed dust pneumoconiosis of comparable severity. Although there appears to be no dose-response relationship in general between silicosis and lung cancer, it is advisable to consider the possibility that a presumptive silica-induced carcinogenesis might be masked by the severe fibrosis of a silicotic type, which obliterates the lung tissue in a different way from asbestosis, which is associated with epithelial proliferation.