WT1 as a complementary marker of malignant melanoma: an immunohistochemical study of whole sections.

AIMS: To test the usefulness of WT1 as a diagnostic aid in melanoma diagnosis and prognostication. METHODS AND
RESULTS: Benign naevi, Spitz naevi, dysplastic naevi and melanoma in situ, primary epithelioid, spindle cell and desmoplastic melanoma, and metastatic melanoma biopsy specimens were collected. Primary melanoma cases were grouped using the 2003 Tumour Node Metastasis classification. Cases were examined using haematoxylin and eosin and WT1-stained sections. The presence and pattern of WT1 expression were recorded. Benign naevi were uniformly negative with WT1. The majority of Spitz naevi expressed WT1 (83%). The dysplastic naevi/in situ group showed expression of WT1 in 35% of cases. The majority of primary epithelioid melanoma cases showed WT1 expression (88%). The prevalence of expression by each T category was similar, with T1 = 90%, T2 = 75%, T3 = 95% and T4 = 90%. All spindle cell and desmoplastic melanoma cases showed WT1 expression (100%). Ninety per cent of metastatic melanoma cases expressed WT1.
CONCLUSIONS: WT1 is a useful ancillary diagnostic tool in routine melanoma diagnosis. WT1 expression in primary melanoma is unrelated to tumour depth. Its usefulness is limited by the fact that most Spitz naevi express WT1, up to one-third of dysplastic naevi can express WT1 and not all melanomas demonstrate its expression.