Basing Treatment Strategy for Non-functional Pancreatic Neuroendocrine Tumors on Tumor Size

Background. Surgical resection is advocated for all stages of pancreatic neuroendocrine tumors (PNETs); whether small PNETs can be managed by observation alone is controversial. Methods. The prognoses of patients with non-functional PNET managed by surgical resection or observation alone were retrospectively analyzed. In patients who had undergone resection, correlation of pathologically assessed tumor extension and grade with tumor size were evaluated. Results. Nineteen patients with PNET of median tumor diameters of 12 mm (range 6-38 mm) were followed up by observation for 19-162 months. Increase of tumor size >20 % occurred in three patients, resulting in 5-year progression-free survival of 83 %, but no distant metastases occurred. Surgical resection was performed in 71 patients. Tumor size correlated with the incidence of lymph node or hepatic metastases, portal vein invasion, and Ki-67 index. None of the 18 patients with a tumor size <= 15 mm developed lymph node or distant metastases, and all these patients survived without recurrence for 5-283 months. The smallest tumor size with lymph node metastases was 19 mm. The 5-year recurrence-free survivals of patients with a tumor size <= 15 mm (100 %) was significantly better than patients with tumor sizes 16-20 mm (86 %), 21-30 mm (71 %), 31-50 mm (83 %), and >50 mm (48 %). Conclusion. Because PNETs <= 15 mm in size have little risk of metastases or recurrence, careful observation with serial image studies is acceptable. Once the tumor size exceeds 15 mm, the risk of metastases and recurrence increases significantly.