Immunohistochemical characterization of pulmonary blastoma.

The immunohistochemical staining patterns of three pulmonary blastomas (PBs) were studied for markers of mesenchymal (vimentin, muscle-specific actin) and epithelial (cytokeratin, epithelial membrane antigen) differentiation to clarify their phenotypic nature and, possibly, their histogenesis. Epithelial markers were confined to the tubular component of the tumors, and the mesenchymal markers were confined to the stromal component, demonstrating that PBs are true mixed tumors. These findings are consistent with origin from a primitive pluripotential stem cell but do not rule out derivation from a single germ layer with subsequent metaplastic transformation.