C80-22 Unmasking the Unlikely: Renal Cell Carcinoma as a Rare Culprit of Recurrent Malignant Pleural Effusion

Introduction Approximately 15% of patients with cancer develop malignant pleural effusion (MPE). The majority are due to lung and breast cancers, comprising 50-65% of MPE. In 5-10%, no primary malignancy is found. MPE due to renal cell carcinoma (RCC) is exceedingly rare, accounting for <1% of all MPE. Here we describe a case of recurrent MPE due to RCC. Case Report A 70-year-old man presented to an outside hospital for dyspnea. He was found to have bilateral pleural effusions and underwent a left-sided thoracentesis which revealed malignant cells of unclear primary. He was discharged home but presented to our institution a week later with recurrent dyspnea and new hypoxia requiring oxygen. He was afebrile, sinus tachycardic to 110 bpm and normotensive. Exam was notable for obesity and bilateral lower extremity pitting edema. Chest x-ray revealed bilateral left greater than right pleural effusions and bilateral hilar lymphadenopathy. He underwent a repeat left-sided thoracentesis with 1.8L of bloody fluid removed. Pleural fluid studies demonstrated a lymphocyte predominate exudate. Microbiology studies were negative. Cytology revealed papillary renal cell carcinoma cells. Due to recurrent symptomatic MPE, an indwelling pleural catheter was placed in the left pleural space. A CT abdomen/pelvis identified a left renal mass, osseous lesions and widespread thoracic and retroperitoneal lymphadenopathy, which were FDG-avid on PET. A biopsy of a retroperitoneal lymph node confirmed papillary renal cell carcinoma. He was initiated on Nivolumab and Cabozantinib. Discussion RCC often metastasizes to the lungs; however, metastatic pleural involvement is rare. When observed, it is late in the disease process and is associated with high grade papillary and clear cell tumors. In approximately 10% of MPE, no primary tumor can be identified. Advanced diagnostics have improved identification of these unknown primary tumors. A classic autopsy and case series review found pleural metastases from RCC in only 1-2% of metastatic renal cell cases. MPE due to RCC occurs even less frequently, mostly described in clinical case reports, accounting for <1% of all malignant pleural effusions. This case contributes to a small body of literature describing pleural involvement of metastatic RCC. References: https://publications.ersnet.org/content/errev/31/166/220053 https://pubmed.ncbi.nlm.nih.gov/35576996/ https://www.atsjournals.org/doi/full/10.1164/ajrccm.162.5.ats8-00 https://pubmed.ncbi.nlm.nih.gov/26525375/ https://pubmed.ncbi.nlm.nih.gov/16240395/ https://pubmed.ncbi.nlm.nih.gov/4016683/ This abstract is funded by: None