Fig. 4

Histopathological examination. Proliferation of atypical cells, mainly signet-ring-like cells, in the appendix mucosa is observed using haematoxylin–eosin staining (A). Abundant mucus is confirmed using alcian blue staining (B). Immunohistochemical staining for chromogranin A (C) and synaptophysin (D) are negative in the cytoplasm of tumour cells. The immunoactivity for synaptophysin reveals nerve fibre proliferation in the mucosa of appendix. Immunohistochemical staining for insulinoma-associated protein 1, which is nuclear marker of neuroendocrine differentiation, is negative in the tumour cells (E). Immunostaining for CK (AE1/AE3) highlights the cytoplasm of the tumour cells and normal epithelium (F). Proliferation of spindle-shaped cells from the lamina propria to the lower layer in the colon is noted (G), and the neural marker (CD56) is positive (H)