Diagnostic utility of IMP3 in segregating metastatic melanoma from benign nevi in lymph nodes

Depending on the Breslow depth of the primary melanoma, sentinel lymph node biopsy is considered as standard of care for the staging of cutaneous melanoma, and is one of the most important prognostic factors. The histologic analysis of these specimens becomes difficult to interpret when benign intranodal nevic cells mimic metastases. Insulin-like growth factor-II messenger RNA (mRNA)-binding protein-3 (IMP3), also known as K homology domain-containing protein overexpressed in cancer or L523S, is a member of the insulin-like growth factor-II mRNA-binding protein family and has been shown to have diagnostic utility in distinguishing cutaneous melanoma from benign nevi. In this study, 43 sentinel lymph node biopsy specimens, including 13 with benign intranodal nevi and 30 with metastatic melanoma (two cases containing both benign nevi and metastatic melanoma), from 41 patients were immunohistochemically analyzed with a monoclonal antibody against IMP3. None of the benign intranodal nevi expressed IMP3, whereas 21 out of 30 (70%) of the lymph nodes containing metastatic melanoma did. It seems that IMP3 is helpful in distinguishing benign intranodal nevi from metastatic melanoma in sentinel lymph node biopsy specimens, and could be a valuable diagnostic adjunct in sentinel lymph node biopsy assessment in which questions arise as to the malignancy of the melanocytes present. Modern Pathology (2009) 22, 1582-1587; doi:10.1038/modpathol.2009.128; published online 4 September 2009