Pulmonary atypical carcinoid tumor with marked alphafetoprotein production and features of an adenocarcinoma differentiation.

A 67-year-old man presented with a pulmonary atypical carcinoid tumor with marked elevation of the serum alpha-fetoprotein (AFP) level to 181,000 ng/ml and no hepatic metastases. Immunohistochemistry revealed AFP-positive fine granules, sparsely distributed in some cells. The proportion of the concanavalin A nonbinding subfraction was 33.7%. Light microscopy revealed hyaline globules within or outside the clear and reticular cytoplasm of a few cells. These were ultrastructurally electron-dense materials similar to the hyaline bodies observed in yolk sac tumors. The Grimelius silver method stained only a few cells and very few cells showed a positive Masson-Fontana reaction. Electron microscopy revealed secretory granules measuring 220 nm on the average in scattered cells. Immunohistochemical studies showed 5-hydroxytryptophan in many cells and 5-hydroxytriptamine or serotonin in only a few cells. As for polypeptide hormones, gastrin was detected and in autopsy specimens carcinoembryonic antigen (CEA) immunoreactive cells were observed. Past case reports on the coexistence of carcinoid tumors and adenocarcinomas in the digestive tract suggest that the tumor cells in our case are also derived from primitive or stem cells of endodermal origin and expressed unusual differentiation in the course of treatment.