S3861 Hilar Mass Presenting as Isolated Colorectal Cancer Metastasis

Introduction: Colorectal cancer remains as one of the most common cancers that are diagnosed and remains as significant contributor to morbidity and mortality. Despite advances in techniques, improving access to diagnostic modalities and increasing awareness, it often presents at a later stage and can recur despite treatment. Recurrence can be variable and can occur years after treatment. Liver is the most common location for metastasis to occur. We present an unusual case of recurrent colorectal cancer that occurred several years post treatment and presented as an isolated metastasis to the hilum of the liver leading to biliary obstruction without any other identifiable lesions including in the colon itself. Case Description/Methods: 68-year-old man with prior mucinous adenocarcinoma of the rectosigmoid (pT3N1b, 2017) treated with rectosigmoidectomy and adjuvant chemotherapy, and another primary mucinous adenocarcinoma of the cecum/appendix (2021) treated with segmental colectomy, appendectomy, and chemotherapy, presented to the Emergency Department with jaundice and elevated liver enzymes. A recent high-quality colonoscopy 3 months prior showed only 3 diminutive tubular adenomas. On exam, he appeared frail and cachectic with scleral icterus and bradycardia. Right upper quadrant tenderness was present. Labs revealed bilirubin 3.4 mg/dL, alkaline phosphatase 230 U/L, alanine aminotransferase 215 U/L, aspartate aminotransferase 95 U/L. Prior liver function tests from a few months prior were normal. Computed tomography (CT) abdomen revealed severe intrahepatic biliary dilation with a suspected lesion at the common hepatic duct; the distal common bile duct was normal in caliber. MRI/MRCP identified a soft tissue mass at the biliary confluence with no focal hepatic lesions. Small 4 mm stable subpleural lung nodule seen previously was unchanged. Due to concerns about ERCP complications, patient opted for external biliary drainage by interventional radiology, during which cytology samples were obtained. Pathology revealed adenocarcinoma with immunohistochemistry positive for CK20 and CDX2 and negative for CK7, consistent with colorectal origin. Positron emission tomography-CT revealed no definitive FDG uptake suggestive of malignancy or other active disease. Medical and surgical oncology teams were consulted and he is pursuing further care at dedicated pancreaticobiliary center. Discussion: Metastatic adenocarcinoma of colon presenting as an isolated hilar mass is extremely rare and can mimic cholangiocarcinoma. Accurate diagnosis requires high clinical suspicion and tissue confirmation to guide management.