RESUMO
Over the last 8 years, a 5-fold increase in the incidence of mice with spontaneous hepatoblastomas and a moderate increase in the incidence of chemically induced hepatoblastomas in B6C3F1 mice occurred in 2-year NTP studies compared to the previous 7 years. There was a positive association between an increased incidence of mice with hepatoblastoma and an increased incidence of mice with hepatocellular tumors in the treated mice. The rate of pulmonary metastases for hepatoblastoma was similar to that of pulmonary metastasis for hepatocellular carcinomas. Although a variety of chemicals caused an increased incidence of mice with hepatoblastoma, there was no apparent association between a specific chemical structure or a biological class of compounds and their capacity to induce hepatoblastomas. Hepatoblastomas frequently arose within hepatocellular carcinomas or adenomas and were induced by the same compounds that induced hepatocellular neoplasms. Therefore, it seems reasonable to combine the incidence of mice with hepatoblastomas and the incidence of mice with hepatocellular carcinomas in hazard identification studies.