Cancer progression is facilitated by blood coagulation. Anticoagulants, such as Hirudin and low molecular weight heparins (LMWHs), reduce metastasis mainly by inhibition of thrombin formation and L- and P-selectin-mediated cell-cell adhesion. It is unknown whether the effects are dependent on cancer cell type. The effects of anticoagulants on tumor development of K1735 and B16 melanoma cells and CT26 colon cancer cells were investigated in mouse lung. Tumor load was determined noninvasively each week up to day 21 in all experiments using bioluminescence imaging. Effects of anticoagulants on tumor development of the three cell lines were correlated with the fibrin/fibrinogen content in the tumors, expression of tissue factor (TF), protease activated receptor (PAR)-1 and -4 and CD24, a ligand of L- and P-selectins. Hirudin inhibited tumor development of B16 cells in lungs completely but did not affect tumor growth of K1735 and CT26 cells. Low molecular weight heparin did not have an effect on K1735 melanoma tumor growth either. TF and PAR-4 expression was similar in the three cell lines. PAR-1 and CD24 were hardly expressed by K1735, whereas CT26 cells expressed low levels and B16 high levels of PAR-1 and CD24. Fibrin content of the tumors was not affected by LMWH. It is concluded that effects of anticoagulants are dependent on cancer cell type and are correlated with their CD24 and PAR-1 expression.