Tyrosinase immunoreactivity in formalin‐fixed, paraffin‐embedded primary and metastatic melanoma: frequency and distribution

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Abstract
Monoclonal antibody T311 specifically detects tyrosinase protein expression. Tyrosinase‐derived peptides are recognized by CD8+ T‐celis and applied in immunotherapy. We examined formalin‐fixed paraffin‐embedded tissue of 50 melanoma (primary n=31, metastatic n=19) and 41 control cases (junctional, dermal, compound, Spitz, Reed, balloon‐cell nevi) by immunochemistry using the alkaline phosphatase‐anti‐alkaline phosphatase method after antigen retrieval. Staining with mAb T311 showed a sensitivity of 94% for melanoma with a very high specificity for melanocytic cells. Immunopositivity (94% of melanomas overall) correlated inversely with clinical stage: clinical stage I and stage II showed 100%, stage III and stage IV 86% immunoreactivity each. Staining changed from an exclusively homogeneous pattern in early stages to a more heterogeneous pattern in later stages. Melanocytic control tissue like nevi of different subtypes all showed weak to moderate, homogeneous immunoreactivity with polarity towards the epidermis. RT‐PCR ELISA analysis of short‐term melanoma cell cultures displayed mRNA expression in only half of the originally immunopositive tumors only, suggesting rapid mRNA expression loss in culture. mAb T311 allows detection of melanoma‐associated tyrosinase protein expression and thus profiling of melanomas using routine archival tissue suited for immunotherapy approaches involving tyrosinase derived epitopes.