Simultaneous diagnosis of well-differentiated neuroendocrine tumor and gastrointestinal stromal tumor of the stomach: an infrequent finding.

We present the case of a 75-year-old female patient who was referred to gastroenterology consultation due to vitamin B12 deficiency. Anti-parietal cell and anti-intrinsic factor antibodies were positive. An upper gastrointestinal endoscopy was performed for the suspicion of autoimmune gastritis, identifying in the greater curvature of the gastric corpus a 25 mm spherical, subepithelial lesion, suggestive of gastrointestinal stromal tumour (GIST). A 2 mm sessile polyp was observed adjacent to it. Biopsies from both lesions were taken. Histological examination of the submucosal lesion showed mucosa with neuroendocrine cell dysplasia. The polypoid lesion was compatible with a well-differentiated neuroendocrine tumour (G1) with affected margins. A SPECT-CT scan was performed, showing the lesion compatible with GIST expression of somatostatin receptors. There were no signs of distant extension. Using endoscopic ultrasound, the subepithelial lesion was described as a hypoechoic bulge of the fourth layer, measuring 25 x 18 mm. It was not possible to visualize the polyp. EUS-guided fine needle aspiration was performed, and cytology was negative for malignancy. Finally, it was decided to perform an atypical, laparoscopic gastric greater curvature resection. Neuroendocrine tumours (NETs) are epithelial neoplasms derived from cells of the diffuse neuroendocrine system. Gastrointestinal stromal tumours (GISTs), although they represent 1-3% of gastrointestinal neoplasms, are the most common mesenchymal tumours, arising from interstitial Cajal cells. The synchronous finding in the stomach of a well-differentiated NET and a GIST is rare, having been described in a low percentage of cases.