Pulmonary blastoma with rhabdomyosarcomatous differentiation: an electron microscopic and immunohistochemical study.

Pulmonary blastoma is a rare lung tumor composed of epithelial and mesenchymal elements; the latter element may show various patterns of differentiation toward mature tissue, such as cartilage, smooth muscle, and bone. Rhabdomyoblastic differentiation in pulmonary blastoma is quite rare; only five such cases have been reported. We report two cases of pulmonary blastoma with rhabdomyoblastic differentiation documented for the first time by electron microscopy and immunohistochemistry including documentation for myoglobin, actin, vimentin and desmin. The diffuse and prominent rhabdomyoblastic differentiation in one case is most unusual.