Enhanced tumor growth in Rras^−/− mice. (A) Approximately 10⁵ B16-F10 cells were injected subcutaneously into Rras^+/+ (n = 7), Rras^+/− (n = 9), and Rras^−/− (n = 7) mice in a B6;129Sv genetic background. Images from representative tumors induced after 3 weeks are shown. White arrowheads indicate tumors. Bar represents 0.5 cm. (B) Tumor incidence (%) is shown with the number of animals with palpable tumors indicated. Statistical analysis was performed using Fisher χ² (P values). (C) Tumor volumes were measured at week 3. Data derived from 2 independent experiments with 3 to 6 mice each. Bars represent median. **P < .005. (D) The kinetics of tumor growth is shown. Bars represent SE. **P < .005. ns indicates not significant. θOne Rras^+/+ animal was removed because of mortality. δOne Rras^−/− animal was removed from incidence analysis because of damaged tumor. φTwo Rras^−/− mice with either tumors that have exceeded humane endpoint (> 2 cm in diameter) or damaged were excluded from tumor volume analysis.