CTSK and Osteochondroma: The delayed cartilage tumor onset and growth and the expanded growth plate cartilage in old SHP2KOBglap mice could be explained by the relatively weak activity of Bglap-Cre, which would prolong the time needed to excise both SHP2-floxed alleles, in contrast to the robust activity of Col2α1-Cre and Ctsk-Cre in cartilage.60,63 The time lag for osteochondroma development could also reflect the time required for mutations in other genes to occur and manifest themselves in benign tumor formation.