Abstract

Background: Clear Cell Sarcoma of Soft Tissue (CCSST), or melanoma of the soft part, is a rare, aggressive tumor that originates in the aponeurosis and fasciae of the distal parts of the extremities. Reports from other sites of the body are rare. Objective: We are reporting an extremely rare tumor that presented as a central left-sided lung mass and found to be clear cell sarcoma of soft tissue. Methods: We report a 24-year-old male patient presented with recurrent attacks of left-sided chest pain associated with cough and dyspnea. Results: Imaging showed a central left-sided 8*5.5*5 cm lung mass. The age of the patient and the radiological characteristics of the lesion were suggestive of a benign pathology. After histopathological assessment of the lesion, suspicion of the malignant process was raised, mainly melanoma of soft part and PEComa. The patient underwent left-sided pneumonectomy. The postoperative histological examination, immunohistochemical findings including positive staining for S-100, HMB-45, and Melan-A, and positive FISH study for EWSR1 gene rearrangements supported the diagnosis of CCSST originating primarily in the major fissure of left the lung. Conclusion: The rarity of CCSST in general and tumors originating in the lung primarily raise the challenges in hypothesizing a differential diagnosis, choosing proper investigations and treatment methods. The histological examination, immunohistochemical, and cytogenetics of the tumor are mandatory to reach the final diagnosis.

Key words: Clear cell sarcoma, primary pulmonary melanoma, EWSR1 gene rearrangement.