Epithelioid Inflammatory Myofibroblastic Sarcoma: Case Series With a First Report of CLTC::ALK Fusion in an Aggressive Disease.

Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is a rare and clinically aggressive variant of inflammatory myofibroblastic tumor (IMT). It typically presents in children and young adults, often affecting the abdominal cavity. It is characterized by the presence of plump, polyhedral, and epithelioid cells, and a distinctive nuclear or perinuclear ALK staining on immunohistochemistry. Various ALK fusion partners have been identified in EIMS, including RANBP2, RRBP1, EML4, and VCL. In this report, we present four cases of EIMS involving the abdominal cavity, including the first case with a CLTC::ALK fusion, which has previously been associated only with nonaggressive IMT.