Immunoreactivity of CD99 in invasive malignant melanoma.
BACKGROUND
CD99, also known as p30/32, is a glycoprotein product of the MIC2 gene. It was originally utilized in immunohistochemistry as a unique marker for Ewing sarcoma, other primitive neuroectodermal tumors, and subsequently in other tumors. Its expression in malignant melanoma (MM) has not been well documented, with just two isolated cases of MM recently reported. Recent studies have documented CD99 expression in a significant percentage of atypical fibroxanthomas (AFX), posing potential diagnostic problems in differentiating these two entities. As mistaking MM for AFX based on immunohistochemical staining pattern has significant consequences, we sought to determine the percentage of invasive MM in our archives that have this staining pattern.


METHODS
Seventy-eight cases of invasive melanoma were retrieved from our files. Each case was stained with mouse anti-human CD99 and evaluated for membranous expression.


RESULTS
Our evaluation revealed that 47 of 78 MM cases (60%) stain positive for CD99.


CONCLUSIONS
This study is the first to demonstrate, in a large series, the prevalence of CD99 expression in primary cutaneous melanoma. Additionally, this introduces in the histologic differential diagnosis of CD99 expressing dermal spindle cell lesions.
Wilkerson
Anne E
AE
Department of Pathology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
Glasgow
Meriden A
MA
Hiatt
Kim M
KM
D000071443:12E7 Antigen; D015703:Antigens, CD / Q000096:biosynthesis*; D014408:Biomarkers, Tumor / Q000032:analysis*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D003937:Diagnosis, Differential; D006801:Humans; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D012878:Skin Neoplasms / Q000378:metabolism* / Q000473:pathology; D014973:Xanthomatosis / Q000473:pathology
D000071443:12E7 Antigen; D015703:Antigens, CD; D014408:Biomarkers, Tumor; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules