Penetration of an ascitic reticulum cell sarcoma of the golden hampster into the body wall and through the diaphragm. A scanning electron microscopic (SEM) study.

SEM studies on infiltration of the ascitic form of the hamster reticulum cell sarcoma HaTu 25 into the ventral body wall and through the diaphragm were performed during 6 consecutive days after intraperitoneal transplantation. The findings allow an interpretation of the course of events based on 3 main stages: 1) Contraction of mesothelial cells with partial exposure of the submesothelial stratum. 2) Preferential attachment of tumor cells to these denuded areas. 3) Advance of tumor cells within defects gradually extening from the submesothelial stratum of the musculature. These stages were more pronounced and took a more rapid course at the peritoneal side of the diaphragm than at the body wall. At the pleural side of the diaphragm the appearance of single tumor cells within widened intercellular spaces of the mesothelium was recorded prior to the onset of penetration at the peritoneal surface. The rapid migration of tumor cells through the diaphragm as well as the particularly intensive tumor infiltration into this organ is thought to be connected with the mechanism of intravasation of tumor cells into the lymphatic plexus of the diaphragm. During the whole sequence of events, HaTu 25 cells were found to have maintained their spherical configuration and characteristic surface architecture. Apparently, growth pressure is of minor or no importance in this spacial mode of tumor penetration, rather the action of proteolytic enzymes elaborated by the tumor cells has to be taken into consideration.