Rectal Neuroendocrine Tumor with Synchronous Pancreatic Metastasis: A Case Report

Gastrointestinal neuroendocrine tumors (GI-NETs) often show hematogenous metastasis, with the liver being the most common metastatic site; however, metastasis to the pancreas is rare.We report a rare case of rectal NETs with pancreatic metastases in a 75-year-old man who presented with a chief complaint of constipation. Imaging and endoscopic findings revealed a rectal submucosal tumor, a pancreatic hypovascular mass, and multiple liver masses. The rectal lesion and pancreatic lesions were diagnosed as neuroendocrine tumors using biopsy and endoscopic ultrasound fine-needle aspiration, respectively. Synchronous rectal NET and pancreatic NET (P-NET) with liver metastasis of either of these two were preoperatively diagnosed. A two-stage surgery was performed, comprising abdominoperineal resection and distal pancreatectomy. Pre-operative imaging findings showed a solitary mass in the pancreas, although the resected specimen contained multiple lesions. Immunohistochemical staining of the resected rectal and pancreatic lesions showed that both were synaptophysin positive and chromogranin A (CgA) negative. Generally, rectal NET cells are positive for synaptophysin and negative for CgA, while the majority of P-NETs are positive for both. The final diagnosis was rectal NETs with pancreatic and liver metastases. Till date, there have been no reports on the outcomes in patients with pancreatic metastasis of GI-NETs.More case reports on metastatic NETs are needed to arrive at a consensus for a standardized treatment regimen.