Expression of macrophage/histiocytic antigens in pleomorphic xanthoastrocytomas.

Pleomorphic xanthoastrocytoma (PXA) is a rare variant of a superficial cerebral astrocytoma characterised by distinct clinical and histological features. Its derivation from subpial astrocytes has been proposed, although the capacity of neoplastic cells for expression of different immunohistochemical markers is still under debate. These immunohistochemical studies were performed on eight cases of PXA in order to evaluate the expression and co-expression of glial and macrophage/histiocytic markers in various tumour cell populations. The expression of antigens was examined with the use of single- and double-immunolabelling methods for GFAP, vimentin, LCA, CD68, HLA-class II and MAC 387. All the cases of PXA showed variable immunoreactivity to GFAP, both in spindle-shaped and pleomorphic lipidised tumour cells. A subset of neoplastic cells was stained strongly with HLA-class II monoclonal antibody and with antibody to CD68. The reactivity to LCA and MAC 387 was absent in neoplastic cells, while it was easily evidenced in the non-neoplastic infiltrative component. The immunohistochemical double staining demonstrated the co-expression of GFAP and HLA-class II or CD68 antigens in the cytoplasm of individual neoplastic cells, including large pleomorphic, lipid-laden ones. It seems that tumour cells in PXAs derived from subpial astrocytes reveal monocyte/macrophage immunophenotype and demonstrate the capability of functional behaviour as mesenchymal cells with phagocytic activities. The variability in expression of antigens related to glial and monocytic/macrophage differentiation stressed the immunophenotypic heterogeneity of tumour cells in PXAs.