Mesothelioma relative to asbestos, radiation, and methylcholanthrene

The carcinogenicity of chrysotile asbestos fibers (Canadian and Rhodesian) for the mesothelium of pleura and peritoneum of NEDH rats was explored by injection of 2 mg of asbestos fibers suspended in saline intratracheally, intrapleurally, or intraperitoneally, with or without ancillary radiation treatment (1,000 rad to the whole body of parabiont rats or 2,000 rad to the right thorax of single rats), or alternatively, by injection of asbestos plus 1 mg of 3-methylcholanthrene. A highly significant incidence of mesothelioma (3.8%) was noted in 159 rats treated with asbestos alone, as compared with 0.1% in 1,417 control rats. Additional treatment with radiation or 3-methylcholanthrene increased this incidence to 11.8% and 25.5%, respectively, the latter increase alone being significant at the .01 level of probability.