Metachronous Pancreatic Metastasis from Rectal Cancer that Masqueraded as a Primary Pancreatic Cancer: A Rare and Difficult-to-Diagnose Metastatic Tumor in the Pancreas.

BACKGROUND Pancreatic metastasis from colorectal cancer is rare and can masquerade as primary pancreatic cancer. CASE REPORT A 70-year-old male was diagnosed with advanced rectal cancer with multiple liver metastases. After neoadjuvant chemotherapy, he underwent radical surgery for the primary tumor and hepatectomy for multiple liver metastases. Adjuvant chemotherapies and additional surgeries were subsequently required for recurrences in the liver, lung, and lymph nodes. A diffuse hypovascular nodule in the pancreatic head and a solitary liver metastasis were detected 2.5 years after the initial surgery and he accordingly underwent further chemotherapy. However, the pancreatic tumor progressed, invading the pancreatic duct and biliary tract. Obstructive jaundice finally prompted discontinuation of chemotherapy and he underwent biliary drainage. His diffuse and hypovascular tumor was clinically and radiographically diagnosed as a primary pancreatic cancer. Pancreatic resection for the pancreatic tumor and hepatectomy for the liver metastasis were performed 4.2 years after the initial surgery, achieving radiographic and surgical curative resection. Pathological examination of the surgical specimen resulted in a definitive diagnosis of metachronous pancreatic metastasis from his primary rectal cancer. Despite further chemotherapy, his general condition worsened; however, he remains alive 5.4 years after the initial surgery, with best supportive care. CONCLUSIONS Pancreatic metastasis originating from rectal cancer can masquerade as primary pancreatic cancer clinically and radiologically. Multimodality treatment is mandatory for metastatic colorectal cancer. Aggressive surgeries for pancreatic metastasis should be considered if curative resection appears possible radiographically and/or intraoperatively.