Gastric Neuroendocrine Tumors (NET) (Carcinoids): A Quick Mini-Review

Gastric Neuroendocrine Tumors (NET) (Carcinoids) – A Quick Mini-Review

Klaus Mönkemüller, MD, PhD, FASGE, FESGE, FJGES

Professor of Medicine, Department of Gastroenterology, Carilion Memorial Hospital, Virginia Tech Carilion School of Medicine, Roanoke, USA

Figure 1. Spectrum of gastric neuroendocrine tumors (NET, carcinoids). A. NET located in stomach body, type II. Note the “squared” sessile shape with depressed top. NET also have spotty areas of increased vascularity. B. Note the areas of neo-angiogenesis. C. NET are often found in the stomach body, on stomach folds. Note this “broadened” fold with reddish, depressed center. D. This NET located on the pyloric channel was found due to its spontaneous bleeding and protruding aspect. E. NET type I located on stomach fold. F. Close up view revealed an irregular mucosal surface with fatty villous structures. G. These pit pattern can be better appreciated using narrow band imaging (NBI). H. “Typical” type I NET in patient with chronic atrophic gastritis. Notice the hypervascular, sessile lesion in the setting of gastric mucosal atrophy. I. NBI is ideal to show the vascularity of these lesions and demarcate from the surrounding tissue. J. Many NET have a characteristic yellowish color and many superficial vessels. K, L and M. Histology of NET. K. Notice the well-differentiated, organoid arrangement of tumor cells, often appearing as small, uniform, round-to-oval cells with characteristic "salt and pepper" chromatin. These tumors typically arise in the submucosa and can grow in various patterns, including nests, ribbons, trabeculae, or glandular (rosette-like) structures. umor cells are positive for neuroendocrine markers, specifically: chromogranin (M), synaptophysin and INSM1.

Classification and Workup of Gastric Neuroendocrine Tumors

▸ Gastric NETs are classified into three types:

Type 1 (80% of cases, associated with autoimmune atrophic gastritis, pernicious anemia, B12 deficiency).

Type 2 (associated with Zollinger-Ellison syndrome/hypergastrinemia), and

Type 3 (neuroendocrine carcinoma, usually solitary and >1 cm — the most dangerous) (1-3).

▸ Both Type 1 and Type 2 are associated with hypergastrinemia but via different mechanisms. In type 1 the increased gastrin is due to autoimmune atrophic gastritis and in type 2 the elevated gastrin is produced by a tumor (gastrinoma). Type 1 and 2 gastric NETs are usually well-differentiated with low Ki-67 index, multiple, and <1 cm.

▸ A solitary gastric NET is more concerning (Type 3), while multiple lesions suggest Type 1 or 2.

▸ NBI/I-scan/FICE cannot differentiate between Type 1 and Type 2, but advanced imaging endoscopy is useful for identifying additional small NETs that may have been missed on white light.

▸ The typical endoscopic characteristics of gastric NETs are its sessile shape, flat top, yellowish color and hypervascularity (see figure 1).

▸ Differentiation between Type 1 and 2 relies on clinical features, endoscopic appearance, and laboratory tests (gastrin levels, anti-parietal cell antibodies, etc.).

▸ If resected with clear surgical margins and no other NET seen on PET, surveillance endoscopy alone may suffice for Grade 1 NETs.

Grading (WHO):

Grade 1 (G1): < 2 mitoses/10 HPF (high-power fields), Ki-67 < 3%.

Grade 2 (G2): 2–20 mitoses/10 HPF, Ki-67 3–20%.

▸ Smaller carcinoids (< 20 mm) can be usually managed by endoscopic resection. This should be aggressive and aim at R0. Thus, the best method is endoscopic full thickness resection or ESD with intermuscular dissection, as some lesions go as deep as the muscularis propria.

References

Nakamura S, Iida M, Yao T, Fujishima M. Endoscopic features of gastric carcinoids. Gastrointest Endosc. 1991 Sep-Oct;37(5):535-8. doi: 10.1016/s0016-5107(91)70823-7. PMID: 1936831.

Hülagü S, Yilmaz H. Gastric carcinoid tumors Ann Clin Exp Metabol 2017:2:1017.

Chuah SK, Hu TH, Kuo CM, Chiu KW, Kuo CH, Wu KL, Chou YP, Lu SN, Chiou SS, Changchien CS, Eng HL. Upper gastrointestinal carcinoid tumors incidentally found by endoscopic examinations. World J Gastroenterol. 2005 Nov 28;11(44):7028-32. doi: 10.3748/wjg.v11.i44.7028. PMID: 16437611; PMCID: PMC4717049.