Immunohistochemical study of malignant melanoma with HMB-45, antibodies against S100 protein, Melan-A, and tyrosinase

Background: Immunohistochemical confirmation is needed to correctly diagnose malignant melanoma, due to its heterogeneous histological appearance. Objective: In the diagnosis of malignant melanoma, we evaluated the usefulness of recently introduced antibodies against Melan-A and tyrosinase, and compared them with antibodies against S100 protein and HMB-45. Method: Immunohistochemical staining with the above 4 antibodies was performed on 36 cases of malignant melanoma which had been excised. The percentage of positive tumor cells with the semi-quantitative estimation were than graded as follows; 0% = grade 0, 1-25% = grade 1, 26-50% = grade 2, 51-75% = grade 3, 76-100% = grade 4. We regarded grade 0 as negative, and grade 1 to 4 as positive. The association of Breslow thickness with the individual grade of 4 antibodies was then evaluated. Results: 1. Positiveness of the 4 antibodies were as follows; 100% of the antibody against S100 protein, 97.2% of HMB-45, 97.2% of the antibody against tyrosinase, 91.7% of the antibody against Melan-A. 2. A case of a HMB-45 negative melanoma showed a grade 4 for the antibody against S100 protein, a grade 2 for the antibody against Melan-A, and a grade 3 for the antibody against tyrosinase. 3. The Breslow thickness had a significant positive correlation with the individual grade of antibody against Melan-A. Conclusion: In combination with the antibody against S100 protein and HMB-45, the newly developed antibodies against Melan-A and tyrosinase may be useful in the diagnosis of malignant melanoma.