Anaplastic Lymphoma Kinase‐Rearranged Chest Wall‐Undifferentiated Small Round Cell Sarcoma With Massive Pleural Effusion and Rapid Progression: A Case With Autopsy Report

Chest wall sarcomas are rare and may exhibit aggressive behavior, posing diagnostic challenges—particularly in young adults. Although multidisciplinary treatments involving chemotherapy, radiotherapy, and surgery are recommended, prognosis remains poor. We report a case of a 43‐year‐old man referred with left‐sided chest pain, dyspnea, and massive pleural effusion. Cytological analysis of the effusion and biopsy revealed small, round, atypical cells, and initial immunohistochemistry suggested Ewing sarcoma. During workup, the patient's symptoms worsened, tumor lysis syndrome developed, and he died on hospital day 28. Autopsy and extended immunohistochemical testing indicated small round cell sarcoma. Molecular analysis identified an echinoderm microtubule‐associated protein‐like 4 ( EML4 )‐anaplastic lymphoma kinase ( ALK ) fusion gene. The final diagnosis was small round cell sarcoma with EML4‐ALK fusion originating from the thoracic wall. This case highlights the importance of early presentation and timely diagnosis using next generation sequencing to facilitate targeted therapy for ALK ‐rearranged chest wall sarcomas and improve patient outcomes.