Outcome of nonfunctioning pancreatic neuroendocrine tumors after initial surveillance or surgical resection: a single-center observational study.

Background: Current guidelines consider observation a reasonable strategy for G1 or G2 nonfunctional pancreatic neuroendocrine tumors (nf pNETs) ≤2 cm. We aimed to characterize their natural behavior and confront the data with the outcomes of patients undergoing upfront surgery. Methods: Data from patients with histologically confirmed nf pNETs ≤2 cm, managed at a single tertiary referral center between 2002 and 2020, were retrospectively reviewed. Results: Thirty-nine patients (mean age 62.1 years, 56% male) with 43 lesions (mean size 12.7±3.9 mm; 32 grade 1 [G1] and 7 grade 2 lesions [G2]) were managed by careful surveillance. Progression was observed in 15 lesions (35%; mean follow up 47 months). Six patients (18%) underwent secondary surgery because of an increase in tumor size or dilation of the main pancreatic duct; 3 of them had lymph node metastasis in the resected specimen. Surgery was followed by pancreatic fistula in 2/6 patients, 1 of whom died. Fourteen patients (mean age 59 years, 64.3% female, mean size of lesions 11.4±3.1 mm) underwent pancreatic surgery immediately after diagnosis. The surgery-associated complication rate was 57.1% (8/14). Of the 14 patients, 13 remained recurrence free (mean follow up 67 months). Recurrent metastatic disease was observed 3 years after pancreaticoduodenectomy (R0, 15 mm G2 lesion, 0 N+/8 N) in 1 patient. Conclusions: The behavior of small nf pNETs is difficult to predict, as there is evidence for malignant behavior in a subgroup of patients, even after surgical treatment. Optimal management remains challenging, as pancreatic surgery is associated with significant morbidity.