Type I gastric neuroendocrine tumors (gNETs) arise in chronic atrophic gastritis under hypergastrinemic stimulation, are typically indolent, with negligible metastatic potential. They present as multiple, small, mucosal (rarely submucosal) yellowish lesions with ectasic vessels. As most are small, superficial and without distant spread, the mainstay of treatment is endoscopic resection, while ENETS guidelines recommend considering surgery for lesions >2 cm or high grade.

We report an exceptionally rare case of a type I gNET with an extremely unusual morphology—flat and involving almost the entire gastric body—successfully treated by endoscopic submucosal dissection (ESD).

A 56-year-old woman with autoimmune atrophic gastritis underwent gastroscopy. High-definition white-light and virtual chromoendoscopy revealed a subtle, completely flat (Paris 0-IIb) lesion with preserved glandular pattern but prominent, irregular “corkscrew-like” vessels, extending continuously from the proximal to the distal gastric body (≈100 mm). 

Targeted biopsies showed low-grade gNET (Ki-67 1%). Somatostatin receptor PET/CT with ⁶⁸Ga-DOTA-peptides and contrast-enhanced CT excluded metastases. Endoscopic ultrasound (EUS) demonstrated mucosal thickening without submucosal or muscularis involvement.

Given the lesion’s remarkable size, the case was discussed at our multidisciplinary neuroendocrine tumor board. The absence of deeper invasion or metastasis supported an endoscopic approach, and ESD was performed. The lesion margins were carefully marked and en-bloc resection was achieved, yielding a 140 × 35 mm specimen. Histopathologic examination confirmed a well-differentiated, G1 multifocal NET with negative lateral and vertical margins and no vascular invasion. Remarkably, serial sectioning revealed more than 40 microfoci of neuroendocrine proliferation ranging from 0.5 to 5 mm.

Postoperative recovery was uneventful. Follow-up endoscopies at two and six months showed a retracted scar with no recurrence or symptoms.

To our knowledge, this is the first reported case of a giant, completely flat type I gNET successfully removed by ESD. In gNETs, lesion size correlates with lymph-node metastatic risk, typically guiding, for lesion larger than 2 cm, surgical management. However, in this case, careful correlation of morphology, cross-sectional imaging, and EUS findings supported localization limited to the mucosal layer, justifying an endoscopic approach. Definitive histology confirmed confinement to the mucosa and absence of lymphovascular invasion

This case highlights the importance of individualized, multidisciplinary evaluation in gNETs and demonstrates that, even for unusual very large lesions, advanced endoscopic resection can achieve curative results and avoid unnecessary surgery.