Alternative epithelial markers in sarcomatoid carcinomas of the head and neck, lung, and bladder-p63, MOC-31, and TTF-1.

Sarcomatoid carcinomas are rare malignancies which represent poorly differentiated epithelial tumors that may be difficult to recognize as such. While some cases may have obvious epithelial areas, the sarcomatoid areas are poorly distinguishable from true sarcoma at the light microscopic level and, by immunohistochemistry, often show only limited staining for traditional epithelial markers such as cytokeratin or epithelial membrane antigen. This can be particularly problematic for diagnosis on small biopsy specimens. We sought to assess the diagnostic utility of several immunohistochemical markers of epithelial differentiation including p63, MOC-31, and thyroid transcription factor-1 on sarcomatoid carcinomas of the head and neck (19 cases; 'spindle cell carcinomas'), lung (19 cases), and urinary bladder (11 cases). These results were compared to immunohistochemistry for the traditional epithelial markers pan-cytokeratin and epithelial membrane antigen. Staining for p63 showed the greatest diagnostic utility, positive in 63, 50, and 36% of head and neck, lung, and urinary bladder sarcomatoid carcinomas, respectively. p63 stains were positive in many cases where immunohistochemistry was negative for both pan-cytokeratin and epithelial membrane antigen. All three alternative markers were quite specific for epithelial differentiation, each staining less than 10% of the control group of 73 various primary and metastatic sarcomas, melanomas, and benign spindle cell lesions. In conclusion, immunostaining beyond traditional pan-cytokeratin and epithelial membrane antigen may have diagnostic utility in this context.