Giant dermatofibroma with monster cells.

We report a case of a 64-year-old woman with a giant dermatofibroma on her back with the unusual histologic feature of monster cells. The firm, exophytic, 3-cm nodule had purple and yellow components with surface telangiectasia. Histologic examination demonstrated characteristic findings of a dermatofibroma, including rete ridge flattening and bridging; a stroma containing scattered, large, round, eosinophilic collagen bundles; and a polymorphous dermal infiltrate of spindle and xanthomatous cells with scattered siderophages. Some xanthomatous cells demonstrated features consistent with monster cells, including huge bizarre nuclei and one or more nucleoli. Immunohistochemical staining for factor XIIIa was positive. A diagnosis of giant dermatofibroma with monster cells (DFMC) was made. Giant dermatofibromas are rare, with monster cells being an uncommon finding in dermatofibroma. To our knowledge, this is the first report of DFMC.