2221 - External Beam Radiotherapy for Gastroenteropancreatic Neuroendocrine Neoplasms: Long-Term Local Control, Survival and Toxicity

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 27

POSTER

Presenter(s)

Yuan Tang, MD - Cancer Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, Beijing

J. Shuai¹, T. Xu¹, H. Li¹, N. Wang¹, Y. Liu¹, N. Lu¹, N. Li¹, S. Wang¹, Y. Tang¹, and J. Jin^1,2; ¹State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, ²Department of Radiation Oncology,National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China

Purpose/Objective(s): To evaluate local control (LC), overall survival (OS), and treatment-related toxicity of external beam radiotherapy (EBRT) for gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) in a real-world cohort, as EBRT outcomes in this population remain poorly characterized.

Materials/Methods:

We retrospectively reviewed GEP-NEN patients treated with EBRT between 2014 and 2025 at a single tertiary cancer center, where radiotherapy decisions were made through a multidisciplinary team (MDT). Lesion-based LC was the primary endpoint. OS and toxicities graded by CTCAE v5.0 were secondary endpoints. Kaplan–Meier methods were used to estimate LC and OS.

Results:

Twenty-one patients with 26 irradiated lesions were included, with a median follow-up of 48.5 months (range 6.7–144.0). Primary sites were stomach/gastroesophageal junction (42.9%), colorectum (33.3%), pancreas (14.3%), small bowel (4.8%), and duodenal ampulla (4.8%). Histologies included neuroendocrine carcinoma (NEC, 42.9%), mixed neuroendocrine–non-neuroendocrine neoplasm (MiNEN, 33.3%), and G1–3 neuroendocrine tumor (NET, 23.8%); 52.4% had metastatic disease at EBRT initiation. EBRT targets included primary-site/regional targets (including postoperative beds without gross disease) and recurrent/metastatic lesions, located in the abdomen (n=12), pelvis (n=7), bone (n=1), and brain/cord (n=2). Dose–fractionation was site-adapted: liver metastases were treated with hypofractionation (typically 60–66 Gy in 10–15 fractions), whereas most upper-abdominal GI/pancreatobiliary targets (including stomach/GEJ and pancreas) and pelvic targets (e.g., rectum) received conventionally fractionated regimens (typically 45–60 Gy in 25 fractions). All local failures occurred within 12 months after EBRT (0.89–6.18 months). The 1-, 2-, 3-, 4-, and 5-year LC rates were all 83.7%, and the median LC was not reached. At 1 year, lesion-based LC was 90.9% for abdominal GI/pancreatobiliary targets (95% CI, 75.4%–100%; n=11; 1 event), and 100% for pelvic targets (n=7; 0 events) and brain metastases (n=3; 0 events). The 1-, 2-, 3-, and 5-year OS rates were 100%, 88.9%, 75.2%, and 54.7%, respectively. Median OS was 91.0 months (95% CI: 48.5 months–NA). Most toxicities were grade 1–2 (gastrointestinal symptoms, fatigue, and hematologic toxicity). Two patients (9.5%) experienced grade 3–4 hematologic toxicity; no treatment-related deaths were observed.

Conclusion:

In this real-world cohort of GEP-NENs, EBRT achieved durable long-term LC with acceptable toxicity. Local failures clustered within the first year after EBRT, followed by a sustained LC plateau with median LC not reached. These findings support EBRT as an effective local therapy within multimodality management for GEP-NENs, warranting further validation in larger, multi-institutional studies.