Lung tumors with a rhabdoid phenotype.

Six malignant tumors of the lung with a rhabdoid phenotype are described. All presented as lung masses in middle-aged to elderly adults (mean age 51 years), with no sex predilection. The tumors ranged from 1.3 cm to 8.0 cm in size and were generally associated with locally advanced disease. The distinctive (and defining) histologic feature was the presence of macronucleolated tumor cells with a large eosinophilic globular cytoplasmic inclusion. These "rhabdoid" elements comprised at least 10% of the neoplastic population. Immunohistochemistry revealed diffuse vimentin positivity in all cases. Epithelial and neuroendocrine markers were at least focally positive in five and in all six cases, respectively. Electron microscopy was performed in one case and it showed paranuclear aggregates of intermediate filaments, dense core granules, and intercellular attachments. Malignant tumors of the lung with a rhabdoid phenotype are very rare. The majority are poorly differentiated carcinomas, and they frequently show features suggesting a neuroendocrine differentiation.