Confirmatory diagnosis and successive chemotherapeutic treatments of metastatic skeletal EWSR1::NFATC2 sarcoma: A case report.

EWSR1::NFATC2 sarcoma is rare and its clinical features remain unclear. Given the similarity in presentation, it is possible that previously reported cases of Ewing-like adamantinoma may have been EWSR1::NFATC2 sarcoma. The present case report describes a tumor in a 55-year-old man that was originally thought to be a Ewing-like adamantinoma, but was recently found to be an EWSR1::NFATC2 sarcoma following direct sequencing. The patient experienced pain in their left lower leg at 38 years of age. The initial pathological diagnosis was 'epithelioid malignant tumor of the left tibia suggesting Ewing-like adamantinoma'. The patient underwent wide excision of the tumor in their left tibia with left total knee arthroplasty and a medial gastrocnemius muscle flap. Thereafter, the patient continued with no evidence of recurrent or metastatic disease; however, 14 years later, they developed multiple lesions in the left lung, left pleural dissemination, and enlargement of the mediastinal, left hilar and juxtaesophageal lymph nodes. Pathological diagnosis of transbronchial lung biopsy was consistent with 'Ewing-like adamantinoma'. The patient received doxorubicin-based systemic chemotherapy as first-line therapy, which resulted in stable disease. After disease progression, the patient received eribulin monotherapy, which resulted in stable disease for 15 months. Reverse transcription-polymerase chain reaction followed by direct sequencing revealed an in-frame EWSR1::NFATC2 fusion where exon 8 of EWSR1 (ENST00000397938.7) was fused to exon 3 of NFATC2 (ENST00000371564.8), and their diagnosis was changed to EWSR1::NFATC2 sarcoma. The disease progressed, left pleural dissemination progressed, left pleural effusion increased and peritoneal dissemination in the left paracolic gutter was suspected. Therefore, the patient was started on trabectedin monotherapy during 16 months of stable disease, and thereafter received pazopanib after they presented with progressive disease on prior trabectedin monotherapy. It is likely that there are more patients with undiagnosed EWSR1::NFATC2 sarcoma. To make a definitive diagnosis, a thorough investigation should be performed.