Fig. 3

a Hematoxylin and eosin staining. Tumor cells (arrowheads) show nests or trabecular growth, have rich clear cytoplasm and small round-to-oval nuclei with inconspicuous nucleoli, and had no mitosis. b Immunohistochemical staining of chromogranin A. Tumor cells show positive expression. c Immunohistochemical staining of synaptophysin. Tumor cells show positive expression. d Immunohistochemical staining of Ki-67. Tumor cells show Ki-67 index < 1.0%. (a–d: original magnification × 100)