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Background:  Twenty to 30% of malignant melanomas are associated with melanocytic nevi; however, sometimes it is difficult to distinguish the melanoma from the nevus by routine histology. We have previously described distinctive patterns of elastic fibers in nevi and in melanomas.

Methods:  We analyzed elastic fiber patterns using elastin immunostain and elastic van Gieson (EVG) stain in 30 cases of invasive melanomas associated with nevi, 12 control melanocytic nevi and 14 control invasive melanomas.

Results:  Elastin immunostain was superior to EVG in showing the elastic fiber patterns. In nevi, the elastic fibers were preserved between nests and often around individual melanocytes. In contrast, melanomas had markedly decreased elastic fibers in the stroma and within the nests of melanocytes. The melanoma pushed down the pre-existing thin elastic fibers of the papillary dermis, forming a compressed layer at its base, which separated the melanoma from the nevus. On sun-damaged skin, the solar elastosis had similar elastin and EVG patterns. In three cases with dense inflammation, the layer of elastic fibers between melanoma and nevus was still present but less evident.

Conclusions:  The distinctive patterns of elastic fibers, best shown by the elastin immunostain, were helpful in evaluating melanomas associated with melanocytic nevi.