A single-center experience in observation of small pancreatic neuroendocrine tumors: to operate or not to operate?

Abstract

Presenter: Ariana Naaseh BA | University of California, Irvine Background: Pancreatic neuroendocrine tumors (pNET), particularly non-functioning, have gained recent attention due to their malignant transformation potential. The 2019 National Comprehensive Cancer Network (NCCN) Guidelines state optimal management of larger, invasive, or node positive pNET is surgical resection. For small (less than or equal to 2 cm) primary non-metastatic non-functioning pNET observation is recommended in select cases, usually when the tumor is low grade and < 1 cm in size. Decisions to proceed with surveillance versus resection include both consideration of surgical risk and patient co-morbidities as either distal pancreatectomy with or without splenectomy or pancreatoduodenectomy are not without complications. Our study aims to assess whether conservative, non-operative management of small, low-grade non-functioning pNETs is appropriate. Methods: A retrospective review of all patients with a diagnosis of pNET since 2004 referred to our high-volume multidisciplinary hepato-pancreato-biliary center was conducted. Patients with pNET were identified from pre-existing institutional hepato-biliary service database and confirmed via chart review of consultations and follow-up visits, radiologic imaging, and pathology reports. Results: 126 patients were found to have the diagnosis of biopsy-proven pNET. 8 patients were found to have metastatic disease at time of presentation and were excluded from further analysis. Of the 118 patients analyzed, 26 (22.0%) had functioning lesions and 92 (77.9%) non-functioning lesions. All 26 patients with biopsy-proven functioning lesions underwent surgical resection. Of 92 biopsy-proven non-functioning lesions, 36 had lesions less than or equal to 2.0 cm. Of these 36 patients, 31 were observed and 5 underwent an attempt at surgical resection. All 5 operative patients had biopsy-proven Grade 3 lesions. Two of the 5 operative patients were found to have intra-operative metastasis not detected on pre-operative imaging and subsequent resection procedure was aborted. Of the 31 observed patients, 20 (64.5%) were Grade 1 and 11 (35.5%) Grade 2. 10 of the 31 patients (32.2%) had tumor size < 1 cm. The mean follow-up time in months for patients who were observed with lesions less than or equal to 2.0 cm is 27.24 months. Of 31 patients, 24 presented with consistently stable disease on follow up imaging, 7 presented with decreased disease burden (defined as reduction in size or complete absence) and none presented with disease expansion. Of the 7 patients with decreased disease, 5/7 (71.4%) presented with no evidence of pancreatic disease on imaging, despite previous biopsy proven and radiographic proven evidence of disease. Three patients observed with lesions less than or equal to 2 cm died during follow-up, however mortality was not secondary to pNET progression or malignancy. No patients in the non-operative group underwent surgical resection at any time during the follow-up surveillance period. Conclusion: Our retrospective study demonstrates that observation is appropriate for low grade pNET tumors < 1cm, consistent with NCCN guidelines. Additionally, we demonstrate that close observation rather than surgical resection can be considered for non-functioning grade 1 or 2 pNET tumors less than or equal to 2cm, while grade 3 lesions should proceed with surgical resection. Further study is needed to guide standardized management recommendations.