FLT1 and neoplasm: We observe that the isolates contain several subpopulations of tumor cells and tEC: one population of large cells with low levels of VEGFRs; three populations of small cells with low-VEGFR1, mid-VEGFR1, or high-VEGFR1 surface levels; and two populations of small cells with low-VEGFR2 or high-VEGFR2 surface levels.