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Abstract
Purpose: This study aimed to investigate the role of adjuvant radiotherapy (RT) in neuroendocrine tumors (NET) treated with primary resection and systemic chemotherapy and guide to incorporate adjuvant RT based on individualized prediction.

Methods: We identified 4324 eligible patients using the SEER database. The most common histology was small cell carcinoma (SCC), followed by neuroendocrine carcinoma and carcinoid tumor. As the patients treated with RT were not randomly assigned, we performed propensity score matching (PSM).

Results: RT was administered to 1693 (39.2%) patients who had more unfavorable features [higher proportion of SCC, N2/3 stage, and poorly/undifferentiated (PD) tumors]. After PSM, old age, male sex, SCC, advanced T or N stage, PD tumors, large tumor size, and no use of RT were all significantly associated with a poor prognosis. After multivariate analysis, the survival benefit of RT was preserved (HR 0.82, 95% CI 0.73‒0.91, p < 0.001). Exploratory analysis suggested that primary site, PD tumors, SCC, tumor size < 2 cm, or LN negativity were the factors for which adjuvant RT appeared desirable. Further, we proposed a novel scoring system using aforementioned factors; site-thorax/genitourinary, PD tumor, tumor size < 2 cm, LN negativity. Based on individually calculated scores, we found that RT significantly increased survival in patients with scores of 2-4 but not in those with scores of 0-1.

Conclusions: Our study highlights the necessity of guiding adjuvant RT for these rare types of cancer. We proposed a novel scoring system to carefully recommend RT in selected patients.

Affiliations

Jeanny Kwon 1, Byoung Hyuck Kim 2 3
1Department of Radiation Oncology, Chungnam National University School of Medicine, Munhwa-ro 282, Jung-gu, Daejeon, 35015, Republic of Korea.
2Department of Radiation Oncology, Seoul Metropolitan Government Seoul National University Boramae Medical Center, 20, Boramae-ro 5-gil, Dongjak-gu, Seoul, 07061, Republic of Korea. karlly71@snu.ac.kr.
3Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea. karlly71@snu.ac.kr.