Figure 3. Histological features and immunophenotype of tubal intraepithelial metastases from small cell neuroendocrine carcinoma. (A) A large tumor mass involving the uterine cervix shows hypercellular sheets of tumor cells. It infiltrates extensively the cervical stroma. (B) The tumor exhibits multiple foci of coagulative tumor cell necrosis (blue arrows). (C) The tumor cells are small-sized cells with less than the diameter of three small resting lymphocytes. They show indistinct cell border, scant cytoplasm, nuclear hyperchromasia and molding, irregular nuclear membrane, high nuclear-to-cytoplasmic ratio. (D) There are multifocal microscopic foci of metastatic carcinoma along the tubal surface. (E) The mucosal involvement of metastatic carcinoma simulates thickened tubal epithelium, chronic salpingitis, or serous tubal intraepithelial carcinoma. (F) High-power magnification reveals tumor cells possessing scant cytoplasm and hyperchromatic nuclei with salt-and-pepper chromatin, molding, irregular membrane, inconspicuous nucleoli, and mitotic figures (green circle). These histological features of tubal metastatic tumor are identical to those of the primary cervical tumor. (G and H) The tumor cells infiltrate the tubal epithelium. At (G) medium- and (H) low-power magnifications, the nuclear size of tumor cells is similar to or slightly larger than that of lymphocytes and plasma cells. The individual tumor cells extend laterally along the adjacent tubal mucosa and are distributed underneath the normal epithelium, resembling pagetoid spread. (I-L) Immunohistochemically, the tumor cells are positive for (I) CD56 but negative for (J) Wilms tumor 1. (K) Synaptophysin and (L) chromogranin A, both of which are markers of neuroendocrine differentiation, present within the tumor cell cytoplasm. Staining method, A-H, hematoxylin and eosin staining; I-L, polymer method. Original magnification, A, 40×; B, 100×; C, 400×; D, 40×; E, 100×; F, 600×; G, 400×; H, 200×, I, 100×; and J-L, 100×.