Analysis of HMB-45 immunoreactivity in common and cellular blue nevi.

HMB-45 is generally thought of as a melanoma specific antibody; however, there are certain exceptions. It is known that most dermal nevi show no reactivity; however, the dermal nevus component within dysplastic nevi and certain Spitz nevi show positive reactivity. In order to further examine this observation, we undertook a study to examine blue nevi, both common and cellular, for the expression of HMB-45. Cases were stained with antibodies directed at both HMB-45 and S100 protein. Of 16 common blue nevi studied, 14 were positive with HMB-45, as were 6 of 6 cellular blue nevi. Staining for HMB-45 was quite variable in intensity amongst cases labelled common blue nevi. In contrast, cellular blue nevi were uniformly strongly positive. It is therefore concluded that blue nevi, including cellular blue nevi, exhibit an activated phenotype as demonstrated by HMB-45 reactivity.