Polymorphous low-grade adenocarcinoma versus pleomorphic adenoma of minor salivary glands: Resolution of a diagnostic dilemma by immunohistochemical analysis with glial fibrillary acidic protein

Objectives. Differentiating polymorphous low-grade adenocarcinoma (PLGA) fr om pleomorphic adenoma (PA) in salivary gland biopsy specimens from the pal atal region might be a diagnostic dilemma for the pathologist when tumors a re cellular with minimal matrix material. Glial fibrillary acidic protein ( GFAP), expressed by a number of cells in the mature central nervous system, is also expressed in tumors not generally considered to be of glial origin . PAs have previously been reported to strongly express GFAP. PLGAs have be en examined for the expression of this protein only in small group studies with variable results. The objective of this study was to determine whether differential expression of GFAP in these 2 tumors could be diagnostically significant. Study design. A total of 42 PLGAs and 36 PAs, formalin-fixed and paraffin-e mbedded, were immunostained with rabbit polyclonal antibodies to GFAP. CNS tissue was used as a positive control. Results. Results showed the 36 cases of PA to be strongly positive for GFAP. Of PLGA s, 31 were negative and 11 showed faint patchy reactivity in luminal cells. Conclusions. The results strongly support a role for GFAP as a diagnostic a djunct in the microscopic differential diagnosis of PLGA versus PA. This st udy is the largest investigation with consistent results to date addressing the application of this antibody to the diagnostic problem of PA versus PL GA.