CDK4 and fibrous dysplasia: 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.