Undifferentiated carcinoma of the gallbladder. Report of a case with immunohistochemical findings.

One case of undifferentiated carcinoma of the gallbladder was studied using an extensive immunohistochemical panel of antibodies. The biphasic differentiation of the tumor was highlighted by different immunoreactivity to antibodies against cytokeratins, vimentin, epithelial membrane antigen, and carcinoembryonic antigen of the adenocarcinomatous and mesenchymallike components, although the latter showed a faint positivity for CAM5.2 antibody, probably indicating an epithelial origin. Furthermore, the higher levels of expression of p53 protein and the faster growth rate in the pseudosarcomatous component suggest its more malignant phenotype. The relationship with "true" carcinosarcomas of the gallbladder and the histogenetic theories concerning these tumors are also discussed.