A case study of a collision tumor composed of cancers of the bile duct and pancreas

In this case report, we describe the extremely rare case of a collision tumor comprising cancers of the bile duct and the pancreas. A 70-year-old man was referred to our hospital with a diagnosis of obstructive jaundice. He was diagnosed with pancreatic head cancer, and we performed a pancreaticoduodenectomy with lymph node dissection. At laparotomy, there were two palpable masses in the vicinity of the confluence of the cystic duct and the head of the pancreas. The resected specimen demonstrated tumors at the confluence of the cystic duct and in the pancreatic head. Histopathological examination demonstrated a moderately differentiated tubular adenocarcinoma in the pancreatic head and a well-differentiated tubular adenocarcinoma at the confluence of the cystic duct. Immunostaining was negative for p53 and MUC6 in the pancreatic head tumor; however, immunostaining was positive for both in the tumor located at the confluence of the cystic duct. The two tumors were histologically different and were diagnosed as collision cancer caused by the collision of the bile duct and pancreatic cancers.