Detailed information regarding the clinical efficacy of radiotherapy (RT) for primary tumor in patients with unresectable pancreatic neuroendocrine tumors (pNETs) is unknown. We therefore performed a retrospective study to evaluate the efficacy and safety of RT for primary pancreatic tumors in patients with pNETs.

We investigated 11 patients with pNETs who received RT to the primary site between January 1997 and June 2015. Seven patients had Grade 2 neuroendocrine tumors (NET-G2) and four had neuroendocrine carcinoma (NEC) according to the 2010 WHO histopathological classification.

The tumor response and control rates were 27.2% and 100%, respectively (3: partial response, 8: stable disease). Among patients with NET-G2 tumors, the response rate was 28.5% (2/7 patients) and symptomatic improvement was noted in 33.3% of the patients (1/3 patients). The response rate for patients with NEC were 25% (1/4), one NEC patients with symptoms exhibited symptomatic improvement. The median overall survival and median progression-free survival were 35.9 months and 5.5 months, respectively. Grade 3 diarrhea as an acute toxicity and Grade 3 gastrointestinal hemorrhage as a late toxicity were observed.

RT to the primary cancer site in patients with pNETs was an effective modality for local disease control and the treated patients had good outcomes. If metastatic tumors are under control, RT to the primary site may be beneficial for patients with pNETs.