Comparison of Immunohistochemistry for PRAME With Cytogenetic Test Results in the Evaluation of Challenging Melanocytic Tumors.

PRAME (PReferentially expressed Antigen in MElanoma) is a melanoma-associated antigen. Although diffuse immunoreactivity for PRAME is found in most primary cutaneous melanomas, melanocytic nevi express PRAME usually only in a subpopulation of tumor cells or not at all. Hence, testing for PRAME expression has the potential to provide useful information for the assessment for diagnostically ambiguous melanocytic neoplasms. Many of the latter tumors are currently studied by cytogenetic methods for ancillary evidence in support of or against a diagnosis of melanoma. In this study we analyzed 110 diagnostically problematic melanocytic tumors comparing results for PRAME immunohistochemistry (IHC) with those from fluorescence in situ hybridization and/or single nucleotide polymorphism-array, and each with the final diagnostic interpretation. In 90% of cases there was concordance between PRAME IHC and cytogenetic tests results, and in 92.7% concordance between PRAME IHC and the final diagnosis. The high concordance between PRAME IHC and cytogenetic test results as well as the final diagnosis supports the use of PRAME IHC as an ancillary test in the evaluation of ambiguous primary cutaneous melanocytic neoplasms, especially given its practical advantage of lower cost and faster turnaround over cytogenetic or gene expression studies. However, our results indicate that PRAME IHC and cytogenetic tests for melanocytic tumors are not entirely interchangeable and on occasion each type of test may yield false-negative or false-positive results.