Observational study of natural history of small sporadic nonfunctioning pancreatic neuroendocrine tumors

Asymptomatic sporadic nonfunctioning, well-differentiated pancreatic neuroendocrine tumors (NF-PNETs) are increasingly diagnosed, and their management is controversial because of their overall good but heterogeneous prognosis.

The objective of the study was to assess the natural history of asymptomatic sporadic NF-PNETs smaller than 2 cm in size and the risk-benefit balance of nonoperative management.

From January 2000 to June 2011, 46 patients with proven asymptomatic sporadic NF-PNETs smaller than 2 cm in size were followed up for at least 18 months with serial imaging in tertiary referral centers.

Patients were mainly female (65%), with a median age of 60 years. Tumors were mainly located in the pancreatic head (52%), with a median lesion size of 13 mm (range 9-15). After a median follow-up of 34 months (range 24-52) and an average of four (range 3-6) serial imaging sessions, distant or nodal metastases appeared on the imaging in none of the patients. In six patients (13%), a 20% or greater increase in size was observed. Overall median tumor growth was 0.12 mm per year, and neither patients nor tumor characteristics were found to be significant predictors of tumor growth. Overall, eight patients (17%) underwent surgery after a median time from initial evaluation of 41 months (range 27-58); all resected lesions were European Neuroendocrine Tumor Society T stage 1 (n = 7) or 2 (n = 1), grade 1, node negative, with neither vascular nor peripancreatic fat invasion.

In selected patients, nonoperative management of asymptomatic sporadic NF-PNETs smaller than 2 cm in size is safe. Larger and prospective multicentric studies with long-term follow-up are now needed to validate this wait-and-see policy.