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Natural History of Small Pancreatic Lesions Suspected to Be Nonfunctioning Pancreatic Neuroendocrine Tumors

Objectives Nonfunctioning pancreatic neuroendocrine tumors (NF-PNETs) are a rare disease but have been diagnosed more frequently than before. The aim of this study was to evaluate the natural course of small NF-PNETs. Methods We performed a retrospective analysis of patients with incidentally found small NF-PNETs (<20 mm) from 1999 to 2015. The patients who were recommended surveillance were included. Results There were 69 patients with small NF-PNETs with a mean size of 10.9 (standard deviation [SD], 3.1) mm. The average follow-up period was 52.2 (SD, 38.7) months. The changes in tumor size were as follows: increased (13.0%), sustained (84.1%), and decreased (2.9%). Eighteen were evaluated with grade 1 NF-PNETs and 1 with grade 2 among the obtained tissues. Thirteen patients underwent surgery after an average 32.9 (SD, 42.6) months later. There were 7 patients of Ia, 1 of Ib, 2 of IIa, and 1 of IIb according to the pathologic stages. Two patients received reoperation for recurrent tumors, and 2 patients showed distant metastasis after surgery, but no disease-related death occurred. Conclusions: Most of the small NF-PNETs did not increase in size and seldom showed metastasis. The wait-and-see strategy can be used for NF-PNETs less than 2 cm.