Sequence of Events in Experimental Metastases of Walker 256 Tumor: Light, Immunofluorescent, and Electron microscopic Observations2

Abstract

The behavior of Walker 256 tumor cells, reaching the lungs after intravenous inoculation into Sprague-Dawley rats, was studied over a period from a few minutes to 4 days. Serial sections with hematoxylin and eosin, Lendrum's stain for fibrin, and immunofluorescent staining for fibrin were examined, and the same tumor cells were observed by all three methods. Parallel electron microscopic sections followed the progress of similarly injected tumors over the same time period. By all methods it was shown that the cells were arrested singly or in small groups in capillaries and arterioles, and were surrounded by a meshwork resembling fibrin by Lendrum's and immunofluorescent stains, but which appeared only as platelet masses by electron microscopy. Fibrin was identified rarely in the masses by the latter method. The tumor cells remained intravascular for several hours. Platelets disappeared after about 8 hours and there was progressive breaching of the endothelial lining until by 24–48 hours the cells were clearly perivascular and lying in direct apposition to connective tissue. It is suggested that a loose reversible platelet-protein aggregation forms rapidly around the tumor cells, but that stable fibrin is not usually formed with this tumor. During the few hours this aggregation is present the cells breach the endothelium and subsequently become completely perivascular.