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, 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: T1-GNETs showed indolent nature and favorable long-term prognoses. LVI could be useful in indicating the need for additional treatments. Endoscopic resection for risk prediction of LNM should be considered for tumors <10 mm and may be feasible for tumors 10-20 mm.