Interestingly, in transgenic K5-SOS mouse, which develop spontaneous skin papillomas at 100% penetrance, it was demonstrated that depletion of EGFR expression in the mouse entirely prevents tumor formation, due to EGFR inhibition of tumoral cell apoptosis.21 Together, these findings support a synergistic effect of EGFR and VEGF signaling in papilloma development.21 The gene discussed is VEGFA; the disease is skin papilloma.