Metastatic Colonic Adenocarcinoma to the Extrahepatic Common Bile Duct: The Critical Role of the Pathologist and Immunohistochemistry in Guiding Patient Care Decisions.

BACKGROUND Adenocarcinoma of the colon frequently invades adjacent organs, spreads intraperitoneal, and metastasizes to intestinal lymph nodes, lungs, and the liver. Metastasis solely to the extrahepatic bile duct is extremely rare and has only been previously reported on 15 occasions. The accurate determination that an extrahepatic common bile duct lesion is of colonic origin has critical therapeutic implications. CASE REPORT The patient was a 50-year-old male with a history of colon cancer S/P surgical resection in September 2014. At that time, the tumor extended to the serosal margin, and was staged as pT4a N0 MX stage II. In April of 2016, the patientwas admitted to our facility and an ERCP was performed. A biopsy was performed during the ERCP followed by sphincterotomy and metal stent placement. The surgical pathology revealed an adenocarcinoma with surrounding benign glandular structures. The surrounding benign glands served as an appropriate control when compared to the malignant glands. The benign glands were positive for CK-7 and the malignant glands were negative for CK-7. The malignant glands were also positive for CK-20 and CDX-2, and the benign glands were negative for CK-20 and CDX-2. This profile was consistent with an adenocarcinoma metastasis from colon primary tumor. CONCLUSIONS This case superbly illustrates the critical role of the pathologist, and their knowledge and understanding of immunohistochemistry, in arriving at the correct diagnosis and in assisting surgeons and oncologists in guiding the care, management, and appropriate therapeutic decisions regarding patients. In patients with a history of colorectal carcinoma (CRC), immunohistochemistry is required to arrive at the correct diagnosis as treatment options can be very different based on diagnosis.