Polypoid undifferentiated carcinoma with osteoclast-like giant cells arising in the distal common bile duct: A rare case report

Background: Undifferentiated carcinoma with osteoclast-like giant cells (UC-OGC) in distal common bile duct (CBD) is a rare entity. Case report: This case report describes a 45-year-old male with a history of a choledochal cyst status post partial excision and cholecystectomy who presented with a mass in the remaining distal/intrapancreatic common bile duct. It was initially mistaken for post-surgery hematoma; however, the rapid growth raised concern for malignancy, and prompted a pancreaticoduodenectomy (Whipple) procedure. Macroscopic examination revealed a 5.5 cm polypoid mass grossly confined in the lumen of the distal CBD. Histology was consistent with UC-OGC, with minimal invasion into the polyp stalk and adjacent CBD wall. Immunohistochemistry demonstrated co-expression of CK7 and p40, normal/wild-type p53, and retained SMAD4 expression in tumor cells. Next-generation sequencing detected mutations at p.Q61H (c.183A>C) of KRAS and p.E545K (c.1633G>A) of PIK3CA, keeping in line with similarity to conventional cholangiocarcinoma. The patient remained disease-free after two years of follow-up without chemotherapy. Conclusion: To our knowledge, this is the first case report of UC-OGC presented as a polypoid mass in the distal CBD. It highlights the complex dynamism and controversial pathogenesis of this unique entity, which should be made aware to avoid diagnostic pitfalls.