[A Case of Metastasis to the Pancreas from Colorectal Cancer Which Was Difficult to Distinguish from Primary Pancreatic Cancer].

A man in his 50s underwent laparoscopic sigmoid colectomy for sigmoid colon cancer with liver metastasis(cT4aN1M1a, cStage Ⅳa), followed by partial liver resection(S4, S6). One and a half years after the initial surgery, CEA and CA19-9 increased, and contrast-enhanced CT and MRI showed a hypovascular lesion with dilation of the distal pancreatic duct in the pancreatic body. Adenocarcinoma was detected by brushing cytology of the lesion and pancreatic juice cytology by ERCP. From the results of various examinations, the lesion was diagnosed as pancreatic ductal adenocarcinoma. We performed distal pancreatectomy, and initially the histopathological diagnosis was pancreatic body cancer(pT3N1aM0, pStage ⅡB). In a follow-up CT after surgery, a suspected metastatic lymph node was pointed out in the mediastinum, but it was difficult to distinguish between metastasis from colorectal cancer and one from pancreatic cancer. Immunostaining of the tumor tissue and comparative study of the excised specimens of colon and pancreas was performed in order to assume the primary lesion of the lymph node. As a result, both tissues were CK7(-)/CK20(+), and the lesion at first considered to be primary pancreatic cancer was originally the pancreatic metastasis from colon cancer. Bone metastases were also found on FDG-PET/CT around the same time, and then systemic chemotherapy for colorectal cancer was introduced. Four and a half years have passed since the first surgery, and he is still alive and undergoing treatment.