Small-cell carcinoma combined with adenocarcinoma of the gallbladder. A case report with immunohistochemical and flow cytometric studies.

A small-cell carcinoma combined with adenocarcinoma of the gallbladder was detected in a 71-year-old Japanese woman. A nodular mass measuring 4.0 x 5.0 cm was located in the fundus of the gallbladder, in which a tiny depressed lesion measuring 2 mm in diameter was macroscopically and stereomicroscopically observed. Histologically, the depressed area revealed small-cell carcinoma that consisted of atypical cells with small, round to oval nuclei and scanty cytoplasm and was surrounded by ordinary well-differentiated adenocarcinoma. Immunohistochemically, the tumor cells in an adenocarcinomatous area were diffusely positive for carcinoembryonic antigen and showed an interspersed positivity to serotonin and gastrin, while the tumor cells in the small-cell carcinoma area were negative for both antigens. The nuclear DNA content of the tumor cells of both components was aneuploid; however, the first G0/G1 peak of the small-cell carcinoma was much smaller than that of the adenocarcinoma. These results indicated that the tumor revealed a divergence in functional differentiation, and this feature suggested an initial phase of composite small-cell carcinoma and adenocarcinoma in the gallbladder.