Glial fibrillary acidic protein (GFAP) is a major constituent of glial cytoplasmic intermediate filaments.
Glial fibrillary acidic protein expression has been accepted as a marker of astroglial differentiation or origin. However, GFAP expression has been demonstrated in a variety of normal and neoplastic tissues outside the central nervous system, including
pleomorphic adenomas,
chordomas, bone, and cartilage. It has been postulated that coexpression of GFAP and
vimentin in neoplastic myoepithelial cells in
pleomorphic adenomas reflects early chondroid differentiation.
Glial fibrillary acidic protein expression in chondromyxoid and chordoid
tumors was studied in
formaldehyde solution-fixed,
paraffin-embedded sections of 20
pleomorphic adenomas and 10
chordomas by the immunoperoxidase method with the use of commercially available monoclonal (n = 2) and polyclonal (n = 1)
antibodies. All
pleomorphic adenomas and
chordomas demonstrated expression of GFAP with the use of the polyclonal antibody (Biomeda Corp [Foster City, Calif]). Variable expression of GFAP was present in 90% (18/20) and 70% (14/20) of
pleomorphic adenomas, and in 20% (2/10) and 0% of
chordomas, with the use of the two monoclonal preparations (Dakopatts [Glostrup, Denmark] and BioGenex Laboratories [San Ramon, Calif]), respectively. Normal brain tissue and eight
astrocytomas were used as "controls" to compare staining intensity and quality between the polyclonal and monoclonal anti-GFAP
antibodies.
Glial fibrillary acidic protein positivity with the polyclonal antibody was more intense than that with either
monoclonal antibody despite similar (congruent) distributions of
tumor cell types that were stained in control brain and
astrocytoma tissues. The GFAP polyclonal antibody was more frequently immunoreactive than the
monoclonal antibodies, particularly in cells that exhibited chondroid differentiation. These findings may have practical application in surgical pathology.