Metastatic rate of liver tumors induced by diethylnitrosamine in mice.

The metastatic capability of liver tumors induced in 220 C57BL/6J × C3HeB/FeJ F1 mice by diethylnitrosamine was studied. Microscopically primary liver tumors showed a predominantly trabecular pattern with varying degrees of cellular atypia. The invasion of the portal vessels by tumor cells was seen occasionally. Detailed histological examination of the lung tissue revealed metastatic foci in 22% of animals bearing primary liver tumors. Tumors metastasized mainly by the hematogenous route; the metastases were multifocal, often of microscopic size, with isolated foci showing a tendency to coalesce and form larger tumor masses. Areas of diffuse infiltration of the lung parenchyma were also seen. The metastatic capability of diethylnitrosamine-induced liver tumors further substantiated their frank neoplastic nature. Detection of high rate of lung metastases was made possible only through the detailed examination of the whole lungs, regardless of whether or not macroscopic changes were present at autopsy.