Transmission and scanning-electronmicroscopy of experimental liver metastases derived from intrasplenically growing primary tumor.

Liver metastasis formation from intrasplenically growing Lewis lung tumor was studied with transmission and scanning electron microscopy. Tumor cells arrested in the sinusoids formed desmosome-like junctions with endothelial cells and crossed the endothelial lining at intercellular gaps and by transcellular diapedesis. The metastatic foci had no newly formed vessels, and the stroma was provided by non-parenchymatous liver cells. Morphology suggested different outcome for tumor cell-host cell interactions at different stages of tumor growth. The host cell activity to destroy tumor cells was present only at the early stage but disappeared later, when the tumor cells were ready to phagocyte normal cells. The reason for this could be the immunosuppressive effect of the primary tumor. Results emphasize the importance to study metastasis formation in primary tumor-bearing hosts.