Superficial ALK-Rearranged Myxoid Spindle Cell Neoplasm With Aberrant Keratin Expression and a Rare Gene Fusion Partner

Superficial ALK- rearranged myxoid spindle cell neoplasms/epithelioid fibrous histiocytoma (SAMS/EFH) are newly defined hybrid soft tissue tumors within the broader class of S100 and CD34 coexpressing spindle cell tumors that harbor receptor tyrosine kinase fusions. Several research groups have contributed to describing and characterizing the morphologic and immunophenotypic spectrum of SAMS/EFH and exploring its relationship with other similar appearing and molecularly driven neoplasms. To further expand the knowledge of this entity, we present a unique hybrid case of superficial ALK- rearranged myxoid spindle cell neoplasm/EFH with novel aberrant cytokeratin expression and rare ALK::PRKAR1A fusion, thus, adding to the spectrum of such unique and newly emerging tumors.