Protein gene product 9.5 (PGP9.5) immunoreactivity in salivary gland tumors

PGP9.5 is a neuron specific protein with a molecular weight of 245 kDa and is expressed in neuronal cytoplasm and neuroendocrine cells, and is a marker of neuronal differentiation in normal and neoplastic tissues. The present study was designed to evaluate expression of PGP 9.5 in salivary gland tumors and its possible correlation with the expression of S-100, NSE and GFAP1 the other markers predominantly present in nerve tissues. Forty cases of pleomorphic adenoma and 10 cases of salivary adenocarcinoma were evaluated by three stage avidin-biotin-immunoperoxidase method using polyclonal antibody raised against PGP9.5. In normal salivary glands (n=6), PGP9.5 was confined to the peripheral nerve fibers. The non-luminal tumor cells in the tubuloductal structures of pleomorphic adenoma (n=40) showed spindle shaped modified myoepithelial cells expressing PGP9.5 with varying intensity of staining as well as S-100 protein, NSE and GFAP. A variant of modified myoepithelial cells, the plasmacytoid cells were intensely positive for PGP9.5, S-100 protein and NSE. One adenocarcinoma (1/10) showed a strong immunostaining for PGP9.5 in neoplastic cells. It is, therefore, suggested that the salivary gland tumors are composed of cells of heterogeneous differentiation: the luminal tumor cells are purely epithelial origin and characteristics, and modified myoepithelial cells express markers of neuronal differentiation and may arise from the cells of neural crest origin.