Comparison of cytokeratin expression in primary and metastatic carcinomas. Diagnostic application in surgical pathology.

Metastatic poorly differentiated carcinomas often represent diagnostic difficulties in surgical pathology. Therefore, the expression of cytokeratins of different molecular weights (54, 57, and 66 kd) were compared in paraffin sections of 37 primary carcinomas with their lymph node metastases by an avidin-biotin complex (ABC) method, using monoclonal antibodies. The epithelial tumors consisted of 16 squamous cell carcinomas (SCCs) and 17 adenocarcinomas with different degrees of differentiation (well, moderately, or poorly differentiated), a renal cell carcinoma, a hepatocellular carcinoma, a transitional cell carcinoma of the bladder, and a carcinoid tumor of the stomach. The primary and metastatic tumors showed the same cytokeratin profiles. All SCCs and their metastases were positive for 57-kd cytokeratin and negative for 54-kd cytokeratin. All adenocarcinomas and their metastases were positive for 54-kd cytokeratin and negative for 66-kd cytokeratin. The extent of reactions varied with the differentiation of the carcinomas, with well-differentiated tumors showing more diffuse staining. Cases of lymphoma, sarcoma, and melanoma were negative for the three types of cytokeratins. The results indicate that identification of different molecular weight cytokeratins may be used to distinguish poorly differentiated SCCs from poorly differentiated adenocarcinomas, even in metastatic tumors. In addition, demonstration of these cytokeratins is useful in substantiating presence and identity of small foci of metastases in lymph nodes.