While in vivo studies have not directly demonstrated that inactivation of the ERK1/2 pathway is sufficient to produce cartilage tumors, studies have shown that inactivation of Erk1 and Erk2 in mesenchymal cells leads to ectopic cartilage clusters in the perichondrium of mouse embryos [14]. The gene discussed is MAPK3; the disease is chondrogenic neoplasm.