Comparative Histopathological Diagnosis of Cutaneous Melanoma by H&E, Special Staining and Immunohistochemical Methods against Cutaneous Squamous Cell Carcinoma in Horse and Bovine

Abstract

Background: The aim of this study was to compare the role of special staining and to test melanoma associated antigens against paraffin embedded bovine and equine melanomas in order to assess their ability and utility as diagnostic tools for diagnosis and confirmation of the melanomas. Methods: From 1991-2012, 13 cases were reviewed histologically, and each case was found to contain a large focus of melanoma and squamous cell carcinoma (SCC) on the hematoxylin and eosin–stained tissue section. All cases had documented cutaneous melanoma and SCC. Serial 5 μm-thick sections were cut from routine formalinfixed paraffin blocks of 4 case cutaneous SCC (including 2 cases from horses and 2 cases from cattle) and 9 case cutaneous melanomas (including 6 horses cases and 3 cattle cases) from the files of the Department of Pathology have been diagnosed by H&E staining method. For diagnosis confirmation, Fontana-masson silver method, melanin bleaching method and immunohistochemical staining for S-100 protein and HMB45 antigen were applied. Majority of cases encompassed intradermal histologic pattern. Results: In 6 cases out of 9 tumors, both S-100 protein and HMB45 staining methods were positive, whereas there were suspicious results for 3 cases. In all cases, results of Fontana-masson silver and melanin bleaching methods were positive. In 4 cases of squamous cell carcinoma, results of 3 tests were negative. Diagnosis of suspicious melanoma tumor cases must be confirmed or reconfirmed by special staining methods and/or immunohistochemical method. Conclusions: The standard of practice in diagnosing melanoma is to use a panel of antibodies consisting primarily of S-100 protein and HMB-45. For spindle cell and desmoplastic melanomas, however, S-100 protein and HMB-45 should remain within antibody panel since S-100 protein is most sensitive marker for these entities and evidence is lacking that either Melan-A or Mitf are better markers than HMB-45 for recognizing spindle cell melanocytic lesions.