Pulmonary blastoma. Comparison between its epithelial components and fetal bronchial epithelium.

Three cases of pulmonary blastoma exhibiting biphasic epithelial and stromal patterns, and a case of fetal lung-type adenocarcinoma, were examined by immunohistochemistry and electron microscopy (EM) and compared with fetal bronchial epithelium in order to explore the multidirectional differentiation of their epithelial components. The glandular cells of all four tumors resembled fetal bronchial epithelial cells in the pseudoglandular stage. Neuroendocrine (NE) cells were also present; they were argyrophilic and expressed pan-NE markers, neurosecretory granules and peptide hormones. The neural cell adhesion molecule (NCAM) was strongly expressed on the cell membranes of glandular cells, as in the case of proximal bronchial epithelial cells at the pseudoglandular stage in fetal lung. Sialosylated Lewis X was also expressed, indicating that the epithelial cells were possibly of endodermal origin. Two of the four cases showed considerable immunoreactivity for alpha-fetoprotein (AFP). The epithelial cells of pulmonary blastomas may occasionally de-differentiate into cells functionally resembling fetal hepatic, foregut and yolk sac cells expressing AFP. Tumor examination by immunohistochemistry and EM suggested that the glandular cells of the tumors may differentiate to some extent like those of fetal large bronchi at the pseudoglandular stage, but there was concordance and discordance in the expression of neuroendocrine and oncofetal markers between blastomatous tumors and fetal bronchial epithelium.