Co-existing Neuroendocrine Tumors in the Ileum and Pancreas: A Clinico-Pathological Challenge.

Ileal (I) and pancreatic (Pan) neuroendocrine tumors (NETs) are among the most common digestive neuroendocrine neoplasms (NENs). Coexisting NETs at both sites are rare, and establishing the primary or metastatic nature of the two lesions may be crucial for the appropriate treatment. We reviewed all the clinical reports of patients with INETs or PanNETs, diagnosed and treated in our ENETS Center of Excellence between 2012 and 2022. We selected patients with a history of synchronous or metachronous neuroendocrine (NE) lesions at the ileum and pancreas. For those with available histological samples from both sites, an immunohistochemistry (IHC) analysis for CDX2, Islet1, and serotonin has been performed. We found seven patients with NET in both the ileum and pancreas. F to M ratio was 4:3, and the median age at first diagnosis was 54 years (42-79). Five cases had synchronous lesions; in 2 cases, PanNETs were diagnosed respectively 8 and 56 months, after INETs. In four patients, with available histological samples from both the sites, a pathologic review and the IHC analysis have been performed, identifying three different scenarios: (i) primary INET metastatic to the pancreas, (ii) primary PanNET metastatic to the ileum, and (iii) synchronous primary PanNET and INET. In our experience, coexisting ileal and pancreatic NENs are rare occurrences. A multidisciplinary evaluation case-by-case and, whenever feasible, a comprehensive histopathological examination are needed to distinguish between metastatic and primary disease, in order to properly treat the patient.