Fig. 2

, Histopathological and immunohistochemical features of mucinous cystadenoma with neuroendocrine differentiation. A, Low-power view (H&E, 40×) of the mucinous cystadenoma; B, High-power view (H&E, 200×) demonstrating monotonous small neuroendocrine cells arranged in solid nests within the stromal component; C, CK7 immunostaining highlights the mucinous epithelium (positive), with negative staining in neuroendocrine cells; D, CK20 is negative in both mucinous and neuroendocrine components; E, Synaptophysin is strongly positive in neuroendocrine cells but negative in mucinous epithelium; F, Ki-67 shows a very low proliferative index (< 2%) in neuroendocrine cells; G, PAX8 is focally positive in both mucinous epithelium and neuroendocrine cells, H, CDX2 shows focal positivity in both components; I, TTF-1 is negative in both mucinous and neuroendocrine cells; J, SATB2 is negative in both components, K, Estrogen receptor is negative in both epithelial components but positive in the stromal (ovarian-type) cells