Cystic pancreatic neuroendocrine tumors: a more favorable lesion?

Abstract

Objective: Pancreatic neuroendocrine tumors (PNET) are predominantly solid lesions with malignant potential. Cystic PNETs are a small subset in which data are scarce. We aim to compare clinical/pathologic features and prognostic implications of cystic versus solid PNET. Methods: Patients with PNET undergoing pancreatectomy between 1988 and -2016 at a high-volume center were retrospectively reviewed. Demographic, clinical, and histopathologic data were collected and analyzed. PNET lesions were defined cystic if at least partially cystic on preoperative imaging or pathology. Results: 347 patients with PNET were identified; 27% (n=94) were cystic. Patients with cystic PNET were older (59 vs. 55 years, p=0.05) and more likely to be men (64% vs. 51%, p=0.04). Cystic PNET were more commonly non-functional (95% vs. 82%, p=0.004), asymptomatic (44% vs. 28%, p=0.009), and located in the pancreatic body/tail (81% vs. 60%, p<0.001) than solid PNET. On multivariate analysis, tumor location alone remained significant. When available (n=149), Ki-67 proliferation index, a negative prognostic indicator, was significantly lower in patients with cystic PNET (Ki-67≤2%: 83% vs. 63%; p=0.02). Nevertheless, cystic and solid PNET had similar sizes, histologic grade, pathologic stage, presence of nodal (21% vs. 31%, p=0.08) and distant (9% vs. 18%, p=0.06) metastasis at the time of resection. Conclusion: This study found a higher than previously published incidence of cystic PNET (27%). Cystic PNET were less symptomatic and located in the distal pancreas. The disparity in Ki-67 index may suggest an improved prognosis. Distinguishing cystic PNET from solid preoperatively may assist in surgical decision-making; further attention is warranted for long-term follow-up.