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

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×).