Nasopharyngeal carcinoma: antikeratin immunohistochemistry and electron microscopy

Eighteen examples of nasopharyngeal carcinoma (NPC), a tumor with potential diagnostic difficulty, were studied retrospectively. Using the WHO classification, 16 cases were undifferentiated carcinoma (UC). Immunohistochemistry for each tumor was performed on paraffin sections using two commercially available polyclonal antisera and a monoclonal antibody, AE-1. Method 1 used trypsinization, overnight incubation with the primary antibody and the avidin-biotin complex (ABC) technic. Method 2 used a 20-minute incubation with the primary antibody without trypsinization and employed the peroxidase-antiperoxidase (PAP) technic. Method 2 is the one most frequently employed by pathologists who use immunohistochemistry as a diagnostic aid. Method 1 gave clear positive results in each case with antibody AE-1 and, in most cases, with the polyclonal antisera. Electron microscopy in 10 cases demonstrated desmosomes in each case and easily demonstrable tonofilaments in five. The results of this study indicate that in the diagnosis of UC, the most common variant of NPC, squamous differentiation can be documented readily by electron microscopy and immunohistochemistry for keratin proteins. With the latter, optimization of technic is essential for reliable results.