COL2A1 and chondrogenic neoplasm: Lack of Lkb1 within chondrocytes (Col2a1-Cre) of the endochondral skeleton caused cartilage tumors (29), and Ctsk-Cre–expressing cells were identified as the source of metachondroma (28); therefore, Lkb1 loss in Ctsk+ cells was supposed to lead to cartilage tumors.