Multifocal G1-G2 gastric neuroendocrine tumors: Differentiating between Type I, II and III, a clinicopathologic review

Figure 1 The neuroendocrine tumors are seen as minute (less than 1-2 cm) and frequently multiple polyps. A: Gastrectomy specimen with multiple nodules/polyps, ranging in size from 0.5 mm to 2 cm; B: Gastric mucosa showing a neuroendocrine tumor (HE, 40×); C: Nested groups of cells with nuclei showing “salt and pepper” chromatin and no mitotic activity (HE, 400×); D: Ki67 proliferation index of less than 3%, consistent with a well differentiated neuroendocrine tumor G1 (Ki67 immunostain, 200×).

Figure 2 Tumors usually exhibit nil mitotic activity and a low Ki67 proliferation index of less than 3%, compatible with well differentiated neuroendocrine tumors, grade 1. A: A nodule of neuroendocrine tumor nest of cells with nuclei showing “salt and pepper” chromatin with negligible mitotic activity and absent necrosis (HE, 400×); B: Ki67 proliferation index of 5%, consistent with a well differentiated neuroendocrine tumor G2 (Ki67 immunostain, 400×); C: Nest of tumors cells, arranged in nodules, showing intermediate grade cytological atypia characterized by abundant amphophilic cytoplasm, enlarged nuclei with open chromatin and nucleoli; D: Ki67 proliferation index of more than 20%, consistent with a well differentiated neuroendocrine tumor G3 (Ki67 immunostain, 400×).