Expression of insulin-like growth factor-II mRNA binding protein 3 (IMP3) in osteosarcoma. Insulin-like growth factor-II mRNA binding protein 3 (IMP3) is one of the RNA binding proteins implicated in mRNA localization and translational control. It is expressed during embryogenesis, as well as in some malignant tumors. Recent studies suggest its potential use as a prognostic factor or as a therapeutic target in malignancy. Using tissue microarray, we examined the immunohistochemical staining of IMP3 in osteosarcoma cases to evaluate whether it could serve as a prognostic biomarker. In a tissue microarray analysis of 47 paraffin-embedded osteosarcoma cases, 8 (17.02%) were positive for IMP3 immunostaining, and IMP3 expression was correlated with tumor metastasis (p = 0.020). IMP3 expression was independent of survival, tumor site, histologic type, age, and gender. These results suggest that IMP3 could be used as an independent prognostic factor for cases of osteosarcoma with a high potential for metastasis.