Oat cell carcinoma of the gallbladder.

Among 448 malignant epithelial tumors of the gallbladder, 19 were classified as oat cell carcinomas. Seventeen cases occurred in elderly women. Eighteen of the patients had cholelithiasis. The neoplasms were highly lethal, metastasizing early and causing death shortly after diagnosis. All 19 patients died as a direct result of the tumors, with liver, regional lymph node, and/or lung metastases. Combination chemotherapy produced objective responses in two patients, the longest survivors of the series (11 and 13 months). The salient morphologic features of oat cell carcinomas of the gallbladder include large size at the time of diagnosis, extensive necrosis, and propensity for submucosal growth. Histologically, these tumors are composed of variable proportions of two cell types, round and fusiform, arranged in solid sheets, cords, or festoons. In areas of necrosis, the deposition of DNA in vessel walls is seen occasionally. Four tumors contained neoplastic glands similar to those present in well-differentiated adenocarcinomas of the gallbladder. These tumors were considered to be a combined form of oat cell carcinoma. With the use of immunoperoxidase stains, focal carcinoembryonic antigen reactivity was demonstrated in three of 11 tumors. Electron microscopic examination revealed neurosecretory granules. Morphologically, these tumors resembled the oat cell carcinomas that occur at other sites.