Metastatic angiomatoid fibrous histiocytoma of the scalp, with EWSR1-CREB1 gene fusions in primary tumor and nodal metastasis.

Angiomatoid fibrous histiocytoma is a rare soft tissue tumor of intermediate biologic potential, predominantly arising in superficial extremities of children and young adults. Less than 5% metastasize. We describe a case of angiomatoid fibrous histiocytoma in the scalp of an 8-year-old boy, which metastasized to a postauricular lymph node 3 years after primary tumor excision. Histologically, primary and metastasis comprised nodules of bland ovoid cells, with primary additionally showing hemorrhagic cavities, fibrous capsule, and lymphoplasmacytic inflammation. Both strongly expressed desmin, with focal epithelial membrane antigen. Reverse transcription-polymerase chain reaction showed EWSR1-CREB1 fusion transcripts in both primary and metastasis. This is, to our knowledge, the first description of genetically proven metastatic angiomatoid fibrous histiocytoma. Angiomatoid fibrous histiocytoma can mimic both benign and malignant lesions, and although most behave indolently, it is important to recognize their metastatic potential.