The fate of people with pleural hyalinosis (plaques): relationship to direct and indirect asbestos exposure.

A follow-up study of persons with pleural plaques was concluded in 1984. The first cohort was made up of employees and retired workers with direct absestos exposure in an asbestos factory (AZ factory) producing heat-resistant textiles, friction engine parts and heat-resistant boards. The raw material was imported chrysotile and small amounts of crocidolite. The follow-up was started in the 1950s. Our second cohort comprised residents selected by radiographic screening in a vast area surrounding the AZ factory who had had indirect asbestos exposure by airborn asbestos fibres. The follow-up period began in the 1970s. A control group consisted of employees and retired workers of a railway repair shop, without exposure to asbestos dust and within a corresponding age bracket. At the time of assessing our results, most of the subjects assigned to all the three groups were no longer alive so we were able to analyse data regarding their life and death. Hyalinosis complicata and pleural mesothelioma (peritoneal mesothelioma in one case) were present and resulted in death only in those with direct asbestos exposure. While lung cancer was among the causes of death in both cohorts with exposure as well as in the control group, its prevalence in the group with direct exposure was significantly higher than in the control group. By contrast, "other neoplasia" was found both in the control group and in exposed persons without any specific prevalence.