摘要Background:The rate of distant metastasis in patients with pancreatic neuroendocrine tumors(PNETs)is 20％-50％at the time of initial diagnosis.However,whether tumor size can predict distant metastasis for PNETs remains unknown up to date.Methods:We used Surveillance,Epidemiology,and End Results(SEER)population-based data to collect 6089 patients with PNETs from 2010 to 2019.The optimal cut-off point of tumor size to predict distant metastasis was calculated by Youden's index.Multivariate logistic regression analysis was used to figure out the association between tumor size and distant metastasis patterns.Results:The most common metastatic site was liver(27.2％),followed by bone(3.0％),lung(2.3％)and brain(0.4％).Based on an optimal cut-off value of tumor size(25.5 mm)for predicting distant metasta-sis determined by Youden's index,patients were categorized into groups of tumor size＜25.5 mm and≥ 25.5 mm.Multivariate logistic regression analyses showed that,compared with＜25.5 mm,tumor size≥ 25.5 mm was an independent risk predictor of overall distant metastasis[odds ratio(OR)=4.491,95％confidence interval(CI):3.724-5.416,P＜0.001]and liver metastasis(OR=4.686,95％CI:3.886-5.651,P＜0.001).Conclusions:Tumor size ≥ 25.5 mm was significantly associated with more overall distant and liver metastases.Timely identification of distant metastasis for tumor size ≥ 25.5 mm may provide survival benefit for timely and precise treatment.