Objectives: The study group comprised a collective of 1,605 patients with malignant mesotheliomas and with lung tissue available for lung dust analyses.
Method: Clinical features, occupational histories, expositions and individual data were evaluated, and the asbestos bodies concentrations (asbestos bodies/cm3 lung tissue or g wet tissue) were determined.
Results: Mesotheliomas developed mainly in men (94.5%). Of the cases, 96.4% were of pleural origin and only 3.3% were peritoneal mesotheliomas. The biphasic subtype predominated (61.3%), followed by the epithelioid type (29.3%). The sarcomatoid subtype was rarely developed (9.4%). Mean age at first diagnosis was 60.4 years. The mean survival time from time of symptom onset was 13.5 months. Patients with epithelioid subtypes had a longer survival time (16.9 months) than those with biphasic (13.1 months) and sarcomatoid subtypes (5.5 months). Of the patients, 73% presented pleural effusions as initial symptoms of the disease. An increased asbestos burden was identified by light microscopy in 84.8% of the patients. There was no association between histological subtypes and the asbestos burden of the lungs. Patients with peritoneal mesotheliomas had distinctly higher asbestos burdens in the lungs than patients with pleural mesotheliomas. There exists no association between lung asbestos burdens and survival times. The mean latency period was 37.8 years. A trend: higher asbestos burden of the lung/shorter latency periods was suggested. About 70% of the patients had a history of occupational exposure to asbestos dust. Most patients worked in the building trade, the locksmith and machine building industries and in the steel and blast-furnace industries. Of the patients, 25.6% had asbestos-associated lung fibroses, in 40.7% of the cases pleural plaques were identified.
Conclusions: The most important causal factor for development of mesotheliomas is still asbestos, primarily amphibole asbestos. The recurring occurrence of mesotheliomas in younger people without known asbestos exposure needs the urgent investigation of other inducing factors for mesotheliomas.