Expression of KIT (CD117) in biphasic pulmonary blastoma. Novel data on histogenesis.

Biphasic pulmonary blastoma (BPB) is a rare primary neoplasm of the lung and its histogenesis is still uncertain. It has been proposed that BPB is derived from mesoderm or endoderm. Others suggested an origin from a single pluripotential cell. We present a case of a BPB with emphasis on expression of the stem cell factor receptor KIT (CD117). We describe a 61-year-old male patient with a BPB of the upper right lobe. Immunohistochemical analysis was performed using a panel of several antibodies including anti-CD117. Strong cytoplasmic expression of CD117 was found in the epithelium (cytokeratin-positive) as well as in the spindle cells (cytokeratin-negative). Expression of CD117 in both mesenchymal and epithelial cells suggests a single origin and supports the idea that BPB arises from a pluripotential cell that can differentiate into both stromal and epithelial morphologies. The role of CD117 in the pathogenesis of BPB and its possible therapeutic relevance require further investigation.