GFAP and neoplasm: Expression of intermediate filaments has been assessed in small numbers of equine mammary carcinomas and preliminarily indicates that carcinomas are heterogeneous, with documented examples of tumours expressing CK8 or CK18 (luminal epithelial markers), CK14 (basal marker), pan-cytokeratin, glial fibrillary acidic protein (GFAP) and vimentin, with varying degrees of intensity [3, 28, 139].