CD34 expression in primary cutaneous malignant melanoma: apropos of a case and review of the aberrant melanoma phenotype.

BACKGROUND: The histological diagnosis of malignant melanoma can be challenging. Immunohistochemical techniques may define a critical role in certain cases, specifically in establishing a primary diagnosis of melanoma. CD34 is a hemopoietic stem cell antigen expressed in bone marrow and endothelial cells, and may also be expressed in vascular and spindle cell tumors; it is generally negative in malignant melanoma. CASE REPORT: An 83-year-old white female presented with a 3-4 mm area on her right upper back, which had been present for several years. Histologic sections showed a polypoid distortion by sheets and nodules of transformed amelanotic melanocytes lying in intimate apposition to an attenuated epidermis without a concomitant radial growth phase. Tumor cells were extensively S-100 and CD34 positive and showed focal immunoreactivity with melan-A and HMB-45. DISCUSSIONS: We present a case of malignant melanoma of nodular subtype, which strongly expressed CD34. The spectrum of abnormal phenotypes in malignant melanoma is reviewed, and a possible explanation for the presence of CD34 is discussed. This case demonstrates the potential of malignant melanoma to express CD34, defining an infrequently recognized aberrant phenotype. Whether or not expression of this marker is associated with a more aggressive clinical course remains to be determined.