Effect of deficiencies in endothelial cell PARs on pulmonary metastasis. Mice deficient in PAR1 (Par1^-/-, A) or PAR2 (Par2-/^-, B) and littermate (PAR1) or matched (PAR2, see “Materials and methods”) controls in a C57BL/6 strain background were injected with B16-F10-luc cells via tail vein and pulmonary metastasis determined as in Figure 2. Horizontal lines indicate medians. Note that a second comparison in which Par1^+/+ and ^-/- mice were compared (instead of Par1^+/- and ^-/-) also showed no difference (not shown). P values were determined using Mann-Whitney test. ns indicates not significant; ko, knockout; and wt, wild type.