Preneoplastic foci of altered hepatocytes induced in rats by irradiation with alpha-particles of Thorotrast and neutrons.

Prestages of hepatocellular neoplasms induced in rats by continuous internal alpha-radiation of Thorotrast or by fractionated external radiation with neutrons were studied by cytomorphological, cytochemical and morphometric methods. Irradiation with both Thorotrast and neutrons resulted in a significant increase in the number and volume fraction of foci of altered hepatocytes (FAH), the occurrence of which at 14 months correlated well with the previously reported increased incidence of hepatocellular neoplasms appearing after long lag periods. The morphological and biochemical phenotypes of radiation-induced FAH were similar to those of preneoplastic lesions described earlier in hepatocarcinogenesis elicited by chemicals or viruses.