Sporadic Small (≤20 mm) Nonfunctioning Pancreatic Neuroendocrine Neoplasm: is the Risk of Malignancy Negligible When Adopting a More Conservative Strategy? A Systematic Review and Meta-analysis

Background The management of small (≤20 mm), nonfunctioning pancreatic neuroendocrine neoplasms (pNENs) remains under debate. The European Neuroendocrine Tumor Society guidelines advocate the possibility of a conservative approach. Methods A systematic literature search was conducted to identify all studies comparing the risk of malignancy in small pNENs with respect to large ones (>20 mm). Malignancy was defined based on the presence of nodal metastases. Distant metastases, tumor grading (G2–3), vascular microscopic invasion, stage III-IV, and overall and disease-free survival also were evaluated. The data were reported in two ways: using the risk difference (RD) and the likelihood of being helped or harmed (LHH). Results The search identified only 6 eligible studies with an overall population of 1697 resected pNENs: 382 (22.5%) small and 1315 (77.5%) large. The RD of lymph nodal metastases was −0.26 (95% confidence interval (CI): −0.31 to −0.22; P