Immunohistochemical expression patterns of the microRNA-processing enzyme Dicer in cutaneous malignant melanomas, benign melanocytic nevi and dysplastic melanocytic nevi.

Dicer is an essential cytosolic enzyme necessary for processing pre-microRNAs into mature microRNAs (miRNAs). Although a variety of malignancies have been attributed to perturbations in the miRNA machinery, there has been little research conducted on the role of miRNAs in cutaneous malignant melanoma and its premalignant lesions. In this small pilot study, we therefore investigated the distribution of Dicer by immunohistochemistry in cutaneous malignant melanomas, as well as in benign and dysplastic melanocytic nevi. Dicer was assessed in ten cutaneous malignant melanomas (CMM), benign melanocytic nevi (BMN), and dysplastic melanocytic nevi (DMN), by standard immunohistochemical staining. Semiquantitative analyses determined expression indices (EIs), which associate the conventional area fraction of labeled cells with immunostaining intensity scores, based on visual qualitative examination by two independent observers. Mean EI scores were significantly higher in the CMM group compared to those in the BMN group (p < 0.05). However, EI differences between BMN and DMN as well as between CMM and DMN were not significant (p > 0.05). For CMM we observed a significant correlation of Breslow tumor thickness and Dicer EI (r  =  0.84, p  =  0.022). For all three groups investigated, Dicer-positive staining was primarily located in the epidermis, specifically in melanocytes. By immunohistochemistry, Dicer staining was significantly higher in melanoma cells than in benign melanocytes. This preliminary study indicates that alterations in the miRNA machinery could exist and should be subject of further investigation.