Combined small cell carcinoma with pulmonary blastoma and adenocarcinoma: case report and clonality analysis.

We describe a rare tumor occurring in the left pulmonary lobe of a 71-year-old Japanese man. The tumor, which was resected by left lower lobectomy, measured 65 x 50 x 50 mm. Histologic examination revealed papillary adenocarcinoma in small cell carcinoma, and chondrosarcoma. Also, the blastemal cells were located between the small cell carcinoma and the chondrosarcoma, and intermingled with both components. In blastemal cells, some glands resembled a well-differentiated fetal adenocarcinoma. The tumor was diagnosed as combined small cell carcinoma with pulmonary blastoma and papillary adenocarcinoma according to the 2004 WHO classification. Immunohistochemically, the small cell carcinoma expressed TTF-1, pancytokeratin, CD56, synaptophysin, and S100 protein, while blastemal cells expressed vimentin, desmin, smooth muscle actin, CD56, and S100 protein. To investigate whether the tumor was clonal or not, p53 gene mutation of each tumor component was analyzed by laser-captured microdissection, polymerase chain reaction-single-strand conformation polymorphism and direct sequencing. Despite the histologic complexity, all components showed the same mutation at exon5 of the p53 gene. These results indicate that the tumor was clonal and arose from a relatively primitive cell, and that p53 mutation occurred before histologic metamorphosis or differentiation.