Fingerprint CD34 Immunopositivity

Distinguishing neurofibroma from desmoplastic melanoma: the value of the CD34 fingerprint

We have observed 'fingerprint' immunopositivity in association with perineurioma and neurofibroma. A fingerprint consists of delicate, elongated areas of positive labeling that fall between collagen bundles, thereby creating a whorled configuration that is reminiscent of a human fingerprint. At present, the differential diagnosis between early desmoplastic melanoma and neurofibroma remains challenging in a subset of cases because of overlapping histopathological and immunohistochemical features. To assess whether fingerprint CD34 reactivity could be contributory in this context, we stained 50 desmoplastic melanomas and 50 neurofibromas with CD34. Fingerprint CD34 labeling was present in greater than 30% of the proliferation in 96% (n = 48) of neurofibromas and in only 4% (n = 2) of desmoplastic melanomas. Over two-thirds of the neurofibromas exhibited a CD34 fingerprint involving more than 60% of their surface area. In the two cases of desmoplastic melanoma that showed CD34 fingerprint positivity, the staining was patchy and involved less than 60% of the tumor. In partially staining neurofibromas, areas without a CD34 fingerprint tended to occur in central lobular areas. We conclude that CD34 fingerprint immunoreactivity is useful in distinguishing neurofibroma from early desmoplastic melanoma, especially if the fingerprint involves more than 60% of a tumor's cross-sectional area.