Cystic pancreatic neuroendocrine tumors: A more favorable lesion?

Background: Pancreatic neuroendocrine tumors (PNETs) are predominantly solid lesions with malignant potential. Cystic PNETs are a small subset in which data are scarce. The aim of this study was to compare clinical and biologic differences between cystic and solid PNETs.

Methods: Patients with PNETs undergoing pancreatectomy between 1988 and 2016 at a high-volume center were reviewed retrospectively. Demographic, clinical, and histopathologic data were collected and analyzed.

Results: 347 patients with PNETs were identified; 27% (n = 91) were cystic. Patients with cystic PNETs were generally older (59 vs. 55 years, p = 0.05). Cystic PNETs 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 PNETs. Although cystic and solid PNETs had similar sizes and pathologic stage at the time of resection, Ki-67 proliferation index (Ki-67 ≤ 9%: 98% vs. 85%; p = 0.007), and histologic grade (grade I: 84% vs. 59%; p = 0.009) had less aggressive features in cystic PNETs.

Conclusions: In addition to reporting a higher than previously published incidence of cystic PNET (27%), this study found significant differences in multiple clinicopathologic variables between cystic and solid PNETs. Cystic PNET may be a distinct and possibly less aggressive subtype of PNET yet have similar pathologic stage, recurrence, and survival to solid PNETs. Cystic PNETs require further attention to better understand the true natural history.