PF-04880594 (10 mg/kg) induces ERK phosphorylation and BRAF-CRAF dimerization in multiple epithelial tissues in mice and the induction can be attenuated by PD0325901. PF-04880594 (0-40 mg/kg, twice daily for 3 weeks) induces epithelial hyperplasia in mice and the induction is prevented by PD0325901.