Yoshida et al. (7) explored the use of MDM2 and CDK4 immunohistochemistry for the histologic diagnosis of low-grade OS: all 23 low-grade OS cases expressed one or both markers (100%), with 13 cases (57%) expressing both; in contrast, only 1 out of 40 benign mimics (including fibrous dysplasias, myositis ossificans and other entities, but not OF) was immunohistochemically positive for MDM2 or CDK4. This evidence concerns the gene MDM2 and fibrous dysplasia.