Tumor fluid accumulation occurs in both human cancer and experimental tumor models. Solid tumorsshow a tendency to tumor fluid accumulation because of their anatomical and physiological features and thismay be influenced by molecular factors. Fluid accumulation in the peri-tumor area also occurs in the Dunningmodel of rat prostate cancer as the tumor grows. In this study, the effects of tumor fluids that were obtainedfrom Dunning prostate tumor-bearing Copenhagen rats on the strongly metastatic MAT-LyLu cell line wereinvestigatedby examining the cell’s migration and tumor fluid’s toxicity and the kinetic parameters such as cellproliferation, mitotic index, and labelling index. In this research, tumor fluids were obtained from rats injectedwith 2X105 MAT- LyLu cells and treated with saline solution, and 200 nM tetrodotoxin (TTX), highly specificsodium channel blocker was used. Sterilized tumor fluids were added to medium of MAT-LyLu cells with theproportion of 20% in vitro. Consequently, it was demonstrated that Dunning rat prostate tumor fluid significantlyinhibited proliferation (up to 50%), mitotic index, and labeling index of MAT-LyLu cells (up to 75%) (p<0.05)but stimulated the motility of the cells in vitro.