IMP-3, known as Insulin-like growth factor 2 (IGF-II) mRNA-binding protein 3, is an oncofetal protein that stabilizes IGF-II mRNA for trafficking and plays an important role in cell growth and migration. This 65-70 kDa protein is expressed normally in developing tissues during early embryogenesis in a variety of fetal tissues including the liver, lung kidney, thymus, and placenta, but at low or undetectable levels in normal adult tissues. Recent studies have demonstrated IMP-3 expression in various malignant tumors of the lung, gastrointestinal tract, liver, endometrium, and bladder, while undetectable in adjacent benign tissues. IMP-3 may have a critical role in tumor proliferation, invasion and metastasis, and has been suggested to be an independent marker for poor prognosis in patients with clear cell carcinomas.