ABSTRACT
Squamous cell carcinoma is the most common primary tumor in the head and neck epithelium and is the second most common primary tumor type in the lung. Although morphologically indistinguishable from each other with hematoxylin and eosin stain on histology, the tumors have different protein expression profiles. Using 24 formalin-fixed paraffin embedded squamous cell carcinomas of the lung and 24 squamous cell carcinomas in the head and neck, protein expression for cytokeratin 5/6, kallikrein 7, and elafin was evaluated by immunohistochemistry. All three proteins were found to evidence higher expression in head and neck squamous cell carcinoma as compared with that of squamous cell carcinoma of the lung. The differences in expression may help clinical differentiation between primary tumors of the lung from metastatic tumors to the lung from the oral/laryngeal cavities.