S3401 Isolated Pancreatic Metastasis of Renal Cell Carcinoma Without a Renal Primary

Introduction: Pancreatic metastases account for 2%-5% of pancreatic malignancies, with renal cell carcinoma (RCC) being a common source. While pancreatic metastases from RCC often present years after nephrectomy, isolated pancreatic RCC metastasis without a detectable renal primary is exceedingly rare. We present such a case. Case Description/Methods: A 70-year-old man with treated hepatitis C, well-compensated cirrhosis, and history of hepatocellular carcinoma (HCC) treated with stereotactic body radiation therapy (SBRT) had surveillance imaging, which incidentally revealed pancreatic cysts in the uncinate process and neck. Magnetic resonance cholangiopancreatography showed interval growth of the pancreatic head/neck lesion to 1.6 cm (from 0.7 cm 8 months prior), with stable uncinate cyst. Endoscopic ultrasound (EUS) confirmed both cysts as intraductal papillary mucinous neoplasms. Unexpectedly, EUS identified a 1.8 × 1.7 cm lesion in the pancreatic body. Fine needle biopsy revealed clear cell renal cell carcinoma, positive for keratin 8/18, CA-IX, vimentin, and PAX8, and negative for keratin 7. Compared to the patient’s prior liver biopsy, which favored poorly differentiated HCC due to weakly positive Glypican 3, the pancreatic lesion was histologically distinct. Pancreas protocol computed tomography localized the lesion to the superior border of the pancreas, abutting the main pancreatic duct. No renal masses were found aside from simple left renal cysts, and cyst biopsy was negative for malignancy. No other metastases were identified. The patient had no history of renal disease or malignancy-related symptoms. Distal pancreatectomy and splenectomy were considered but precluded by clinically significant portal hypertension. He was treated with SBRT (40 Gy/5 fractions) and opted for surveillance imaging every 3 months over adjuvant pembrolizumab. Discussion: This case highlights a rare isolated pancreatic RCC metastasis without a known primary. Few such cases have been reported, with other sites including adrenal glands, bone, lung, muscle, and liver. Only 1 other case reports a solitary pancreatic metastasis. Although pancreatic involvement is uncommon (0.25-3% of metastatic RCC cases), metastatic RCC should be considered in the differential diagnosis of pancreatic lesions. This case also highlights the benefit of EUS. Distinguishing primary pancreatic cancer from metastasis can be challenging; tissue sampling with immunohistochemical studies is essential for accurate diagnosis and management.