Pulmonary blastoma with germ cell (yolk sac) differentiation: report of two cases.

Pulmonary blastoma is a rare lung neoplasm of disputed histogenesis and variable biologic behavior. Typical cases contain both epithelial and mesenchymal tissues, and a variety of patterns of differentiation have been described. While expression of oncofetal antigens in these tumors has been noted rarely, a coexisting component of germ cell tumor has not been reported previously. We describe the clinical and pathologic features of two cases of pulmonary blastoma having alpha-fetoprotein production and histologic areas of yolk sac tumor. We also report the finding of immunohistochemical staining of fetal lung tissue for alpha-fetoprotein.