Growth Characteristics of Ascitic Tumor Cells in the Heparinized Peritoneal Cavity of the Mouse.

1. In a large proportion of Swiss Albino mice which had received 3 daily intraperitoneal injections of heparin (25 or 50 units) immediately before inoculation of Krebs-2 ascites tumor, the amount of ascitic fluid and its concentration of tumor cells were consistently and significantly lower than in controls. 2. Macroscopically visible implantation of ascitic cells from the fluid into the peritoneum was considerably reduced and sometimes completely absent in overwhelming majority of heparinized mice (Series II). 3. An additional injection of heparin (twenty-four hours after inoculation) increased these effects (Series III) while heparinization given entirely after inoculation (Series I) induced only wide fluctuations in the extent of ascites tumor growth. 4. Accordingly, inhibition of implantation was considered to be the primary and direct effect of heparinization, which may account for reduction of the amount of ascitic fluid and of its concentration of tumor cells as secondary effects. 5. It was accepted, in the light of research by other investigators and by ourselves, that embedding of free tumor cells within a fibrin clot from the cavitary fluid initiated their implantation into the serosa and that preventive heparinization arrested implantation in this early stage.