The carcinogenic effect of inhaled asbestos fibers.

Inhalation of asbestos fibers is associated with high incidence of lung cancers and pleural or peritoneal mesotheliomas in humans. All of these lesions were successfully reproduced in animal experiment, and it was shown that asbestos neoplasm may occur with or without accompanying asbestosis. Incidence of tumors from crocidolite was nearly three times as high as from chrysotile or amosite. It is possible that different carcinogenic entities are responsible for the causation of lung tumors and mesothelial tumors. Lung tumors seem to depend on the adsorptive capacity of asbestos fibers, allowing other carcinogens (heavy metals, polycyclic hydrocarbons, cigarette smoke) to attain a critical focal concentration. Mesothelial tumors, on the other hand, might arise in response to mechanical irritation by fibers which may become lodged during lymphatic spread. Tissues subject to constant respiratory movement (e.g., pleura or peritoneum) are specifically vulnerable to the latter action.