Epithelioid Inflammatory Myofibroblastic Sarcoma Harboring Ros1-Tfg Fusion; A Case Report

Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is a rare and aggressive variant of inflammatory myofibroblastic tumor (IMT). ALK-RANBP2 fusion is one of the supposed mechanisms for the aggressive biological behavior of this tumor. To the best of our knowledge, we report the first case of EIMS carrying ROS1-TFG fusion which affected a 16 year-old male. The patient presented abdominal pain and nausea that had lasted for 3 weeks. CT scan revealed multiple masses in the abdominal cavity. Microscopically, the resected tumor showed growth of atypical round and epithelioid cells with large nucleoli infiltrated in myxoid stroma admixed with inflammatory cells. Mitotic figures were frequent. Immunohistochemically, the tumor cells were positive for vimentin, desmin, CD30, D2-40, focally positive for SMA, WT1, CD99 but negative for cytokeratin, EMA, or ALK. Ki-67 labeling index was around 30 %. FISH analysis revealed ROS1 rearrangement, but not of ALK. The partner gene fused with ROS1 was identified to be TFG by analysis of RT-PCR and Sanger sequence. Expression of ROS1 protein in the neoplastic cells was confirmed immunohistochemically. The patient did not respond to 3 cycles of chemotherapy, and died of perforative peritonitis due to progression of the tumor. EIMS is known to present typical clinical and immunohistological features with bleak prognosis. When ALK rearrangement is not demonstrated in such cases, ROS1 should be evaluated for the diagnosis and direction of treatment.