Clinical characteristics and long‐term prognosis of type 1 gastric neuroendocrine tumors in a large Japanese national cohort

Objectives Optimal management of type 1 gastric neuroendocrine tumors (T1‐GNETs) remains unknown, with few reports on their long‐term prognosis. This study investigated the clinical characteristics and long‐term prognosis of T1‐GNETs. Methods We reviewed the medical records of patients diagnosed with T1‐GNET during 1991–2019 at 40 institutions in Japan. Results Among 172 patients, endoscopic resection (ER), endoscopic surveillance, and surgery were performed in 84, 61, and 27, respectively, including 27, 77, and 2 patients with pT1a‐M, pT1b‐SM, and pT2 tumors, respectively. The median tumor diameter was 5 (range 0.8–55) mm. Four (2.9%) patients had lymph node metastasis (LNM); none had liver metastasis. LNM rates were significantly higher in tumors with lymphovascular invasion (LVI) (15.8%; 3/19) than in those without (1.1%; 1/92) ( P = 0.016). For tumors <10 mm, LVI and LNM rates were 18.4% (14/76) and 2.2% (2/90), respectively, which were not significantly different from those of tumors 10–20 mm (LVI 13.3%; 2/15, P = 0.211; and LNM 0%; 0/17, P = 1.0). However, these rates were significantly lower than those of tumors >20 mm (LVI 60%; 3/5, P = 0.021; and LNM 40%; 2/5, P = 0.039). No tumor recurrence or cause‐specific death occurred during the median follow‐up of 10.1 (1–25) years. The 10‐year overall survival rate was 97%. Conclusions Type 1 gastric neuroendocrine tumors showed indolent nature and favorable long‐term prognoses. LVI could be useful in indicating the need for additional treatments. ER for risk prediction of LNM should be considered for tumors <10 mm and may be feasible for tumors 10–20 mm. Trial registration The study protocol was registered in the University Hospital Medical Information Network (UMIN) under the identifier UMIN000029927.