Novel tyramide-based tyrosinase assay for the detection of melanoma cells in cytological preparations

Fine-needle aspiration (FNA) has been used as a fast, minimally invasive, and reliable method for the evaluation of enlarged lymph nodes. However, there are some cases where the definitive diagnosis cannot be elicited with morphology alone, especially cases without a known primary lesion. Although immunocytochemical studies may be helpful in some situations, they are often complicated by nonspecific staining. Recently, a novel tyramide-based tyrosinase assay was developed. Since melanocytes, both benign and malignant, produce tyrosinase, we postulated that this assay could be useful as an in situ biochemical diagnostic test. We modified the Perkin Elmer TSA assay, a commercial assay based on tyramide, a tyrosine analog that is a substrate for tyrosinase, for use on air-dried cytological preparations. We validated the assay on cell lines, then tested a small series of melanoma and nonmelanoma cytology specimens. The YUGEN8 melanoma cell line was used to optimize the assay and it showed abundant reaction product, while HeLa cells served as a negative control. All melanoma cytology specimens were positive and all nonmelanoma specimens were negative. These results suggest that this simple, fast, and inexpensive assay is a sensitive and specific method for detection of melanoma cells in cytology specimens. This method may be a useful ancillary procedure for the resolution of challenging melanoma cases. (C) 2004 Wiley-Liss, Inc.