A Combined Small Cell and Spindle Cell Carcinoma of the Lung: Report of a Unique Case with Immunohistochemical and Ultrastructural Studies

: A unique bronchial tumor is reported. The tumor grew as an endobronchial polyp and obstructed the right main bronchus. Histologically the lesion consisted of two different types of neoplastic cells; epithelial small cell nests and atypical spindle-shaped cells. Immunohistochemical studies with a panel of antibodies showed that the small cell nests were immunoreactive for epithelial and neuroendocrine markers. The spindle-shaped cells showed positive staining for smooth muscle actin. Epithelial markers were also positive focally in the spindle cells. Electron microscopy confirmed that the spindle-shaped cells had both epithelial and mesenchymal features. Based on these results, the tumor was considered to be a unique combination of small cell and spindle cell carcinoma.