Prognostic factors for pancreatic neuroendocrine neoplasms (pNET) and the risk of small non-functioning pNET

Background Non-functioning (NF) pancreatic neuroendocrine tumors (pNET) often have an indolent outcome. A consensus to submit patients with large (>2 cm) NF-pNET to surgery already exists; but a conservative approach for small (<= 2 cm) NF neoplasms has been proposed. Aim To identify prognostic factors for survival and progression free survival (PFS) of NF-pNET, evaluating whether surgery may be avoided for small NF-pNET. Subjects and methods Retrospective study of 77 consecutive patients with pNET submitted to surgery, of which 60 were NF. Pathological tissues were revised according to the 2000 and 2010 WHO classifications. Risk factors for survival and PFS were evaluated using the Kaplan-Meier method and the Cox regression model. Results The 8-year cause-specific survival of NF-pNET was 79.3 %. At univariate analysis, high grading, high staging, large tumors, angioinvasion and peri-pancreatic infiltration were significantly associated with a shorter survival; at multivariate analysis only peri-pancreatic infiltration was significantly associated with a shorter NF-pNET survival. Most small NF-pNET were grade 1 (74 %), compared to large NF-pNET (27 %). Distant metastases were present in 29.7 % (n = 11) and 17.4 % (n = 4) of patients with large or small NF-pNET, respectively; among the 19 small NF-pNET without metastasis, five had a local malignancy (lymph node metastasis or local infiltration); thus, 39 % of the 23 NF-pNET, turned out to have a malignant potential. Conclusions Among NF-pNET, large neoplasms were associated with worse outcomes; however, small NF-pNET do not seem to have an invariable benign behavior. Whether surgery should be avoided in all patients with small NF-pNET is questionable.