Many epidemiological and experimental studies have suggested that the respiratory tract is one of the most sensitive organs to
environmental carcinogens. Nevertheless there is little evidence to determine the relationship between a specific environmental
carcinogen and a cell type of
lung cancer, because the cell types of
lung cancer and their relative frequencies are highly complex compared with those of other organs and tissues. In the present paper, occupational
lung-cancer characteristics, which are the clearest in the relation between cause and effect in human
lung cancers, were reviewed in comparison with the results of animal experiments concerned with occupational lung
carcinogens. Through accumulation of histopathological examinations of the
lung cancer cases, the following relationships between cause and cell type were conjectured:
chromium and
squamous cell carcinoma;
asbestos and
adenocarcinoma;
nickel and
squamous cell carcinoma;
beryllium and
small cell carcinoma;
bis (chloromethyl) ether and
small cell carcinoma;
mustard gas and squamous cell or
small cell carcinoma;
vinyl chloride and large cell or
adenocarcinoma;
radionuclides and
small cell carcinoma. The relation pertaining to
arsenic,
benzotrichloride and tar could not be conjectured because of insufficient cases and information in the histological diagnosis. On the other hand, the carcinogenicity of these substances in occupational exposure has been confirmed by animal experiments administered intratracheally or by inhalation studies under relatively higher concentration. As a result of recent refinements of inhalation study, all-day and life-span exposure to extremely low concentrations, such as microgram/m3 orders, of certain substances has been possible. The characteristics of lung
tumors occurring in these animals are rather different from those of human. For example, in mouse, almost all of the malignant lung
tumors developed by
carcinogens are
adenocarcinomas and it is rare to find the
squamous cell carcinoma. Moreover,
small cell carcinoma and
large cell carcinoma have not known to occur in the lungs of rats and mice. Therefore, future research should focus elucidating the specific relationship between cause and cell type of human
lung cancer by means of animal experiments on
lung cancer that give attention to the specificities of each experimental animal and the origin of the resultant lung
tumor.