Comparison of three immunohistochemical stains for melanocytes.

Abstract

Melanoma is a neoplasm that primarily affects the skin. The diagnosis of melanoma is done firstly by routine staining, of a section of the lesion, by haematoxylin and eosin, followed by staining with special stains. However, immunohistochemistry (IHC) is a technique that has a relatively higher sensitivity and specificity. Currently the IHC laboratory uses S100p and HMB45 as immunostains for melanocytic lesions. From various studies, the value of Melan-A, or Al03, as a new immunostain for the detection of melanocytes, has been noted. 79 paraffin blocks of melanocytic lesions were collected from the histology laboratory archives, of which 69 were malignant and 10 were benign. The malignant cases consisted of 30 metastatic melanomas, 15 superficial spreading melanomas, 14 nodular melanomas and 10 miscellaneous lesions. The benign cases consisted of 10 naevi. The sections were stained with S100p using the PAP technique, and HMB45 and Melan-A, for both of which the ABC technique was used. The extent and intensity of the immunostains were noted. S100p p stained the nucleus and cytoplasm of melanocytes in benign and malignant lesions, but also nerve cells and skin appendages. HMB45 stained the cytoplasm of melanocytes of malignant lesions only. Melan-A stained the cytoplasm of melanocytes in benign and malignant lesions. Melan-A proved to be the most sensitive immunostain in both benign and malignant lesions (89% ), followed by S100p (79%) and HMB45 (66%). In malignant lesions, only Melan-A showed 100% sensitivity, followed by S100p (89%) and HMB45 (74%). When a paired student's test was done between Melan-A and S100p, and Melan-A and HMB45, there was a significant difference in extent, but not in the intensity of staining. In conclusion, from this thesis and other studies, Melan-A has been shown to be the most reliable marker for melanocytic lesions.