FLT1 and neoplasm: For example, we see that at 3 weeks, early in tumor growth, of the three populations of tEC, 83% have mean VEGFR1 surface levels of ∼13,100 surface- VEGFR1/tEC; 11% present an average of ∼75,400 surface-VEGFR1/tEC; and 6% present ∼1100 surface-VEGFR1/tEC (Fig. 4A).