Expression of S100a, vimentin, NSE, and Melan A/MART-1 in seven canine melanoma cell lines and twenty-nine retrospective cases of canine melanoma

We evaluated the expression of vimentin, S100a, and Melan A/MART-1 (melanom a antigen recognized by T cells 1) in seven cell lines established independ ently from dogs with canine melanoma. We also compared routine immunostaini ng of 29 clinical specimens from melanoma cases using vimentin, S100a, and neuron-specific enolase (NSE) with staining for Melan A/MART-1 as part of a diagnostic panel. All the cell lines were positive for expression of vimen tin and S-100a. MelanA/MART-1 expression was seen consistently in only two of the seven cell Lines. Staining for Melan A/MART-1 was most intense near areas of heavy melanin pigmentation. All except one of the clinical specime ns were positive for vimentin. S100a was expressed in the majority of both pigmented (15/20, 75%) and amelanotic (8/9, 88.8%) tumors. Seventeen of 29 (58.6%) tumors were positive for NSE. Melan A/MART-1 was expressed in 18/29 (62%) tumors, including 90% of pigmented tumors, but in no amelanotic tumo rs. Intensity of Melan A/MART-1 staining correlated positively with biologi c behavior, with seven malignant tumors showing negative to weak staining a nd 10 benign tumors showing moderate to strong staining. Three malignant tu mors showed moderate to intense staining for Melan A/MART-1. Our results su ggest that expression of Melan A/MART-1 may be unstable in cultured cell li nes. Assessment of both S100a and Melan A/MART-1 expression is useful to co nfirm a diagnosis of canine melanoma, and Melan A/MART-1 may be especially informative regarding the biologic behavior of these tumors.