Histopathologic differences between liver tumors in untreated (C57BL/6 X C3H)F1 (B6C3F1) mice and Nitrofen-fed mice

A comparison was made of the histologic characteristics of naturally occurring and Nitrofen-induced liver tumors in (C57BL/6 X C3H)F1 (B6C3F1) mice. Whereas induced tumors generally consisted of solid sheets or nodules of frequently enlarged eosinophilic hepatocytes containing enlarged and/or hyperchromatic nuclei, the spontaneous neoplasms consisted predominantly of small basophilic cells containing oval or round nuclei and frequently arranged in trabeculae 1--2 cells wide. Within the livers of Nitrofen-treated animals, foci of hepatocytes resembling those within the tumor masses were also observed in the nonneoplastic areas. Metastases were not present in the lungs of any controls, whereas small emboli or large masses of neoplastic hepatocytes were present in incidences up to 29% in treated mice with tumors. This bioassay provides evidence that, in some cases, liver tumors in treated mice are morphologically different from those in controls and suggests that Nitrofen induces unique liver tumors rather than acts as a promoter of spontaneous neoplasms.