Immunohistochemical Labeling of Melanocytic Differentiation Antibodies in Melanocytic Nevi and Malignant Melanomas

Background: Malignant melanoma is the cancer derived from melanocyte and its prevalence and mortality has increased constantly. Recently, newly developed monoclonal antibodies such as antibodies to MART-1, tyrosinase, TRP-1, MITF and NKI-beteb are frequently used in the diagnosis of melanoma. Objective: We evaluated these antibodies to see if there are differences of positivity and expression pattern of immunohistochemical labelings between melanocytic nevi and malignant melanomas. Methods: We have examined 6 antibodies (antibody to S-100, tyrosinase, TRP-1, MART-1, MITF and HMB-45) in their expressions in 8 malignant melanomas and 24 benign melanocytic nevi. Results: No remarkable difference in positivity of staining between benign melanocytic nevi and malignant melanomas was observed. The staining pattern for S-100 protein is homogenous in all melanocytic nevi and malignant melanomas. HMB-45 showed staining confined to the junctional and superficial dermal components in both diseases. Tyrosinase and TRP-1 showed staining confined to the junctional and superficial dermal cells in most benign melanocytic nevi and variable in malignant melanomas. Although more variable patterns were found in the malignant melanomas, MART-1 demonstrated homogenous staining of all cells in the benign lesions. The staining pattern of MITF in melanocytic nevi was principally in junctional and superficial dermal components, whereas it was homogenous in malignant melanomas. Conclusions: It should be stated that none of the melanocytic differentiation antibodies has any diagnostic value in differentiating between melanoma and nevus cells, but new monoclonal antibodies taken together could contribute to the detection of malignant melanoma due to their high specificity and complementary natures.