AACE/ACE disease state clinical review: pancreatic neuroendocrine incidentalomas

Abstract

Incidental detection of pancreatic neuroendocrine tumors (PNETs) has substantially increased over the last decade due to widespread use of advanced imaging studies. Reliable initial imaging-based characterization is crucial for the differential diagnosis from other exocrine neoplasms and to determine the appropriate management plan. Measurements of chromogranin A, pancreatic polypeptide, and calcitonin are recommended for the biochemical evaluation. A thorough medical history needs to be performed to rule out multiple endocrine neoplasia (MEN) type 1. The European Neuroendocrine Tumor Society (ENETS)/Tumor Node Metastasis (TNM) staging system together with a grading based on the Ki-67 proliferation index and mitotic counts has proven to give more appropriate prognostic information than the World Health Organization (WHO)/American Joint Committee on Cancer (AJCC) TNM staging but may still fail to safely differentiate benign from malignant lesions. Poorly differentiated PNETs generally present with metastases and are rarely amenable for resection. Well- or intermediately differentiated tumors ≥2 cm with imaging evidence of malignancy or with a Ki-67 >2% should be resected. It has been suggested that non-MEN related, nonfunctioning, and asymptomatic PNETs <2 cm with a Ki-67 index ≤2% carry a low risk of metastasis and may be observed in the absence of clinical or radiologic criteria of malignancy or progression, especially in older patients. However, because metastases may occur with long delay with smaller PNETS, physicians should consider patient age, lesion location, and the risks of operation, and patients not undergoing surgery need to be closely followed closely.

Fig. 1

Flow-chart for imaging work-up of incidental pancreatic lesions. CT = computed tomography; MPD = main pancreatic duct; MRI = magnetic resonance imaging; NET = neuroendocrine tumor; PDAC = pancreatic ductal adenocarcinoma; PET = positron emission tomography; SCA = serous cystadenoma.