Pulmonary blastoma. An immunohistochemical analysis with comparison with fetal lung in its pseudoglandular stage.

Pulmonary blastomas are believed to be mixed epithelial and mesenchymal tumors that recapitulate the developing lung at 10-16 weeks gestation. The authors compared nine blastomas with ten fetal lungs in the pseudoglandular stage of development with a panel of antibodies to various lung antigens to evaluate immunophenotypic homology. Both blastomas and embryonal lungs showed expression of cytokeratin, epithelial membrane antigen, and carcinoembryonic antigen in their epithelial elements, and both contained scattered chromogranin-positive neuroendocrine cells. Rare surfactant-producing and Clara cell antigen-elaborating cells were identified in both groups. The mesenchymal components of blastomas and fetal lung showed smooth muscle, myofibroblastic, and blastematous differentiation. The blastematous elements demonstrated vimentin and keratin coexpression in four cases, providing some support for the contention that pluripotential blastema may give rise to the epithelial and mesenchymal elements of the distal lobule.