IMP-3 expression in melanocytic lesions.

Background: Insulin-like growth factor-II mRNA-binding protein 3 (IMP-3), a member of the insulin-like growth factor mRNA-binding protein family, is expressed in several human malignancies, including melanomas. However, the expression of IMP-3 has not been explored in melanoma in situ, various histologic subtypes of invasive melanomas and atypical Spitz tumors. Methods: IMP-3 immunostain was performed in 157 melanocytic lesions. Results: Nearly all benign (8/8), dysplastic (8/8) and Spitz nevi (8/9) were negative for IMP-3. Focal IMP-3 positivity was observed in 5/12 melanoma in situ and 4/15 superficial melanomas (Breslow depth <= 1 mm). Half (10/20) of deep melanomas (Breslow depth >1 mm) and 25/52 metastatic melanomas demonstrated strong IMP-3 staining. IMP-3 expression differs significantly between non-desmoplastic melanomas (superficial and deep) and benign or dysplastic or Spitz nevi (p = 0.0427, respectively). Four of 23 desmoplastic melanomas expressed IMP-3 , which was significantly different from deep melanomas (p = 0.0109). IMP-3 stained 7 of 10 atypical Spitz tumors. The difference between atypical Spitz tumors and Spitz nevi was statistically significant (p = 0.0256). Conclusion: A malignant circumstance, such as non-desmoplastic melanoma or atypical Spitz tumor, can be inferred when IMP-3 is expressed, suggesting potential diagnostic value of IMP-3 in melanocytic lesions.