Carcinoid tumors of the gallbladder with adenocarcinomatous differentiation: a morphologic and immunohistochemical study.

Two patients with gallbladder carcinoid tumors with adenocarcinomatous differentiation were examined. In both cases, the tumor contained argyrophilic granules and alcian blue-positive mucin. One contained argentaffin granules and the other showed PAS-positive mucin. Numerous membrane-bound electron-dense neurosecretory granules were demonstrated by ultrastructural study. Immunohistochemistry applied for the tumors clarified the epithelial, hormonal, and metaplastic character. Epithelial tumor markers, i.e., carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA), were positive in these tumors. The neuroendocrine nature was demonstrated by positive results of chromogranin A and neuron-specific enolase (NSE). Hormonal activities were not confirmed in the tumor cells. These results suggested that carcinoid tumors in the gallbladder have a multidirectional differentiation represented by a morphological continuum ranging from carcinoid to adenocarcinoma.