Abstract Introduction CIC::DUX4 Round Cell Sarcoma represents one the rarest forms of undifferentiated small round cell sarcomas, typically arising in the lower extremities of young adults. These tumors often present as painless or painful soft tissue masses and can resemble Ewing sarcoma, though they are histopathologically and genetically distinct. We present a case of a 66-year old man with a remote history of CIC::DUX4 round cell sarcoma, previously in remission for five years, who developed recurrent exudative pleural effusions with negative cytology, ultimately found to have pleural metastasis of CIC::DUX4 round cell sarcoma following tissue analysis from a video-assisted thoracoscopic (VAT) surgery procedure. Case Presentation A 66-year-old male with a past medical history of left hip CIC::DUX4 round cell sarcoma resected five years prior presented with four days of worsening shortness of breath. Initial CT imaging revealed a large right-sided pleural effusion which was drained via thoracentesis yielding 2.5L of exudative fluid with negative cultures. Cytology was not collected during the initial drainage. Despite empiric antibiotics, a repeat chest X-ray demonstrated rapid reaccumulation of the effusion three days later. The patient underwent chest tube placement with cytology studies, which again yielded exudative fluid; however, cytology came back negative for presence of malignancy. Given the presence of loculated effusions noted on a non-contrast CT, cardiothoracic surgery was consulted for VATS with decortication. Tissue pathology from this procedure was reviewed at a tertiary center and, one month later, confirmed metastatic CIC::DUX4 round cell sarcoma involving the pleura. During this time, the patient was treated with broad-spectrum antibiotics and managed with ASPET drains for recurrent fluid collections. Once the diagnosis was established, he was transferred to a sarcoma specialty center, but unfortunately passed away within six days of admission. Conclusion This case highlights a rare presentation of pleural metastasis from CIC::DUX4 round cell sarcoma masquerading as an infectious or inflammatory pleural effusion in an older patient outside the typically affected patient population of young adults. Recurrent exudative pleural effusions with negative cytology and positive past medical history of cancer should raise suspicion for malignancy, even if preliminary studies are unrevealing. Early tissue biopsy is essential when effusions persist despite appropriate drainage and antibiotics. Recognition of this atypical manifestation is critical to avoid delays in diagnosis and to facilitate timely oncologic intervention. This abstract is funded by: None
Nish et al. (Fri,) studied this question.