One of the most controversial aspects of PENs is the prediction of biologic behavior. Factors that adversely correlate with clinical outcome include tumor size (>3 cm), capsular and vascular invasion, and a mitotic rate greater than 2 of 10 per high-power field. Both in cytology and on tissue sections, immunohistochemical analysis is very helpful in distinguishing endocrine, ductal, and acinar tumors. Most, if not all, PENs show positivity for general endocrine markers, including synaptophysin and chromogranin. The tumor in our patient exhibited all the clinicopathological features of a low-grade, nonfunctioning cystic pancreatic endocrine neoplasm.