Increased tumor growth and vascularization of Fgfr-1^−/− teratomas. (A) Growth of Fgfr-1^+/− and Fgfr-1^−/− teratomas in NMRI-nu mice. (B) The volume of the teratomas was determined regularly by measuring with a caliper, allowing estimation of the teratoma growth rate (mm³/day). The difference in growth rate between Fgfr-1^+/− and Fgfr-1^−/− teratomas was statistically different; *P = .007. (C) Staining of teratoma sections for CD31 expression (red). Bars represent 50 μm. (D) Quantification of the CD31⁺ area in Fgfr-1^+/− and Fgfr-1^−/− teratomas. The CD31⁺ area was significantly increased (*P = .002) in the Fgfr-1^−/− teratomas.