Clinicopathological Features and Long-term Prognosis of Purely Cystic Pancreatic Neuroendocrine Tumors: A Single-center Experience

Background: Pancreatic neuroendocrine tumors (pNETs) are heterogenous neoplasms, of which the prognosis varies widely. Purely cystic pancreatic neuroendocrine tumors (C-pNETs) are a small subset of pNETs in which data are extremely rare. This study aimed to compare clinicopathological and long-term survival differences between C-pNETs and solid pNETs (S-pNETs).

Methods: A retrospective review of 242 patients with pNETs underwent resection in our institution from 2009 to 2019 was conducted. Demography characteristics, clinicopathological features and long-term outcomes of them were analyzed.

Results: Sixteen out of 242 patients (6.6%) were identified as C-pNETs. Compared with S-pNETs, C-pNETs were more frequently non-functional (75% vs 45%, P = 0.02), and the median tumor diameter of C-pNETs was smaller (36 mm vs. 47 mm, P = 0.001). And the accuracy of preoperative diagnosis of C-pNETs was significantly lower (31% vs 78%, P = 0.001). Of note, the majority of C-pNETs were well-differentiated with G1 (81% vs 35%, P = 0.001). And there were no G3 (0 vs 7%, P = 0.001) in C-pNETs. No T4 stage or R1/R2 surgical margin detected in C-pNETs. And only one C-pNETs (6%) had regional lymph node metastasis (N) or synchronous distant metastasis (M). Additionally, only one patient with C-pNETs (6%) suffered tumor recurrence, compared with 24 (13%) for S-pNETs. And survival analysis showed the patients with C-pNETs seemed to be with better disease-free survival (P = 0.26).

Conclusion: C-pNETs are rare subtype with possibly less aggressive behavior comparing with their solid counterparts. Recurrence and tumor-related death still occurs in patients with resected C-pNETs, although they tend to be with more favorable prognosis.