Asbestos Exposure - Asbestos Lung Disease

Mesothelioma Cancer Diagnosis

Industrial Health 2001, 39, 189-193
191 ASBESTOS-INDUCED LUNG CANCER COMPLICATED SILICOSIS

Discussion

Asbestos exposure is well known to induce primary lung cancer. On the other hand, the International Agency for Research on Cancer (IARC) recently classified crystalline silica as a human carcinogen2). However, no definite international consensus has been obtained concerning about the carcinogenesis due to silica3).

We4, 5) previously reported a high incidence of lung cancer due to asbestos exposure among shipbuilding workers. The major occupations types of the patients complicated lung cancer were riggers, plumbers, and welders. The patient reported in this study had worked as a caster in a shipyard for 30 years. Casting is a process to produce parts of ships by pouring metals into sand molds, and asbestos is not generally used in this process. The primary component of dust in this process is silica, and thus, silicosis often develops. However, by detailed occupational inquiry, long tubes are often produced in casting in shipyards, and their production includes a process in which asbestos is placed on molds to reduce distortion. Chest X-ray examination and CT scanning of this case showed large shadows probably due to silicosis in the bilateral upper lung fields, which were histologically confirmed. But definite pleural plaques and typical pulmonary fibrosis(honey combing) were not observed on chest CT images, suggesting pulmonary asbestosis.

Therefore a premortal definite diagnosis of asbestosis could not be made. Autopsy revealed definite pleural plaques and pathological findings consistent with pulmonary asbestosis. In addition, 28,000 asbestosis bodies/g (dry weight) of pulmonary tissue, which corresponds to occupational asbestos exposure, were detected. According to the Helsinki criteria, an item for the definite diagnosis of asbestos lung cancer is 5,000 asbestos bodies/g (dry weight) of pulmonary tissue. Our patient fulfilled this criterion. Histopathological examination also showed numerous asbestos bodies around silicotic nodules. These findings suggested that mixed dust of silica and asbestos induced pneumoconiosis in this patient.

We6) and Yasui et al.7) reported about the detection of asbestos bodies indicating occupational exposure in the lungs of patients with silicosis. But we could not confirm the histological pulmonary asbestosis in these previous cases with silicosis. In premortal examinations of this case, we failed to diagnose definite asbestosis, because of the absence of pleural plaque or asbestosis on his chest X-ray. As for the chest X-ray, the grade of asbestosis for this patient was 0/1 from the ILO criteria of pneumoconiosis in 1980. After postmortem examination, this patient was diagnosed as silicosis and asbestosis (silico-asbestosis). A conventional definition of asbestos lung cancer was lung cancer in patients with pulmonary asbestosis. However, several studies8, 9) have indicated no association between carcinogenicity and fibrogenicity of asbestos, and the presence of pleural plaques as an important finding of asbestos-induced lung cancer10-14).

We have suggested the importance of pleural plaques in patients with lung cancer15). This suggestion has been supported by Egilman11) and Hillerdal9) in the 1990s. Indeed, in this patient with pulmonary asbestosis, a definite diagnosis of pulmonary asbestosis could not be made though chest CT scanning showed subpleural curvilinear shadows16). Pleural plaques are readily diagnosed by chest CT at present. In this patient, we could easily detect pleural plaques at autopsy, but could not detect by chest CT scanning. At autopsy, pulmonary fibrosis and pleural plaques were easily detected. We should do autopsy as the cases who had occupational histories of asbestos exposure. Shida et al.17) reported that patients with mixed dust pneumoconiosis(MDP) increased recently according to the change of working environments with low concentration dust, and then the typical silicotic nodules show low as before.

This type of pneumoconiosis induces fibrotic changes in the bilateral inferior posterior lung fields, showing large shadows as observed in this patient. The images in this patient were similar to those of MDP. However, based on a substantial amount of asbestos bodies and pulmonary fibrotic changes, a diagnosis of pulmonary asbestosis, not MDP, could be made. We speculate that cases of silicosis complicated by asbestosis in shipyards may be more common than ever recognized, and such cases will also be appear in the future, and therefore, intend to perform further studies. This patient had been exposed to asbestos dust in his working place for more than 10 years and had lesions consistent with pulmonary asbestosis in the lungs and pleural plaques. In addition, 28,000 asbestosis bodies/g dry weight of pulmonary tissue were detected. He was also a heavy smoker with Brinkmann index of 900. Asbestos exposure and smoking were the important factors for the appearance of lung cancer.

This case was compensated as entitled to Japanese compensation for industrial accidents for asbestos lung cancer. However, he was not entitled to this compensation for silicosis because his silicosis was PR4A and F(+) due to absence of respiratory failure and classified as management 3. Crystalline silica was classified as a carcinogen by IARC in 1997 because of the large body of epidemiologic literature18). In Japan, silica induced lung cancer without severe pulmonary function or large opacities which occupied more than 1/3 of unilateral lung field was not to be compensated for industrial accidents, because crystalline silica has been to have not a definite carcinogenicity by the result of the recent Japanese professional meeting. Therefore, the clarification of asbestos exposure in this patient was of great value for the compensation.

Asbestos Lung Disease

Asbestos exposure can result in the development of an asbestos lung disease. There are two categories of asbestos lung disease; primary lung disease and secondary lung disease. Secondary lung disease develops from a primary lung disease, usually the result of metastasis.

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