Pulmonary well-differentiated fetal adenocarcinoma expressing lineage-specific transcription factors (TTF-1 and GATA-6) to respiratory epithelial differentiation: an immunohistochemical and ultrastructural study.

A case of pulmonary well-differentiated fetal adenocarcinoma was examined with conventional histological, immunohistochemical, and ultrastructural studies that revealed the distribution of lineage-specific transcription factors (TTF-1 and GATA-6). The patient was a 33-year-old Japanese woman, who underwent resection of the right lower lobe for the lung tumor. The tumor demonstrated an organized histology mimicking the epithelial differentiation of fetal lung with peculiar glands and moruloid cell nests, without mesenchymal proliferation. Adenocarcinoma cells forming the atypical glands were similar to the epithelial cells of the branching tubules in the pseudo glandular stage of the fetal lung. Distribution of TTF-1 was observed in many of the nuclei of the adenocarcinoma cells forming the glands. Tumor cells in the morula were primitive epithelial cells with some immunohistochemical neuroendocrine cell differentiation and some of them showed GATA-6-positive stains in the nuclei. In the ultrastructural study, adenocarcinoma cells showed little differentiation toward mucous cells and ciliated cells. Neuroendocrine granules were seen in a few tumor cells in the morula. In the present case, tumor cells forming the peculiar histological, molecular, and ultrastructural constructions showed partial and incomplete mimicry of the morphogenesis of respiratory epithelium.