Undifferentiated carcinoma of the gallbladder. A clinicopathologic, histochemical, and immunohistochemical study of 21 patients with a poor prognosis.

Among 284 cases of carcinoma of the gallbladder, 21 were identified as undifferentiated carcinoma (UC), with little glandular or other specific epithelial differentiation. These tumors were classified into three histologic types according to the components: (1) small cell type (eight cases); (2) pleomorphic cell type (eight cases); and (3) spindle cell or pseudosarcomatous type (five cases). Histochemical and immunohistochemical study by the immunoperoxidase technique revealed that most of the tumors (13/21) contained mucosubstances, and that all examples of the UC were immunoreactive for epithelial membrane antigen (EMA), keratin, and carcinoembryonic antigen (CEA), thereby indicating the epithelial nature of the neoplastic cells. Vimentin immunoreactivity was found in nine tumors. In 19, the tumor contained various neoplastic endocrine cells, including somatostatin-immunoreactive (14/19), gastrin-immunoreactive (14/19), human chorionic gonadotropin (HCG)-immunoreactive (9/19), pancreatic polypeptide-immunoreactive (4/19), and serotonin-immunoreactive cells (4/19). The prognosis of patients with UC of the gallbladder was poorer than that of patients with differentiated adenocarcinoma.