Clinical Prognosticators of Metastatic Potential in Patients with Small Pancreatic Neuroendocrine Tumors.

Background: While observation of T1(≤2cm) nonfunctioning pancreatic neuroendocrine tumors (NF-PanNETs) is an accepted practice, an ill-defined subgroup of patients with T1 tumors develops metastases. This study aimed to identify those patients via clinical factors.

Methods: Patients from the Surveillance, Epidemiology, and End Results (SEER) registry who were diagnosed with NF-PanNET with size ≤2cm between 1998 and 2014 and who underwent primary tumor resection were identified. Binary logistic regression analyses were performed to evaluate factors associated with pathological nodal and systemic metastatic disease.

Results: A total of 612 patients with T1 NF-PanNETs were identified. Of those, 72 (11.7%) developed nodal metastasis and 35 (5.7%) distant metastasis (M1). In the multivariable analysis, tumor location in the pancreatic body (OR 1.903, p=0.03) (OR 1.407, p=0.038) or tail (OR 1.258, p=0.04) (OR 1.612, p=0.021); tumor grade III-IV (OR 2.042, p=0.022) (OR 5.379, p≤0.001); and younger age (OR 0.963, p=0.01) (OR 0.919, p=0.009) were associated with nodal metastases and the presence of M1 disease, respectively.

Conclusion: While the low metastatic potential of ≤2cm NF-PanNET implies watchful waiting to be an appropriate strategy for most patients, the increased risk of metastatic disease in younger patients with high grade (III-IV) body/tail tumors suggests individualized risk stratification to be optimal.