[Significance of immunohistochemistry in neuro-oncology. V. Keratin as a marker for epithelial differentiation of primary and secondary intracranial and intraspinal tumors].

Intermediate filament keratin is regarded as a good marker for epithelial and mesothelial tumors. In the intracranial and intraspinal spaces keratin has been demonstrated only in the endocrine cells of the adenohypophysis, squamous epithelial islands in the pars tuberalis of the hypophysis and in the choroid plexus epithelium. Since gliomas and meningiomas do not express keratin, this marker provides an additional help for differentiating between primary and secondary CNS tumors. Indirect immunofluorescence using an anti-keratin serum was used in a retrospective search for keratin in 80 tumors of the cranium and intraspinal space. Of the primary CNS tumors keratin positivity occurred in craniopharyngiomas, epidermoid tumors, pituitary adenomas, chordomas, a plexus papilloma as well as in the majority of germ cell tumors. Only 3 renal cell carcinoma metastases of 21 metastatic epithelial cell tumors (7 bronchial carcinomas, 6 breast cancers, 6 renal carcinomas, 1 rectum carcinoma, 1 cervix carcinoma) were keratin-negative. Similar findings were made in two melanoma metastases which we examined, whereas in a seminoma metastasis a few keratin expressing cells were found. Primary CNS tumors such as myxopapillary ependymomas, medulloepitheliomas, malignant meningiomas and paragangliomas which are often difficult to distinguish from these metastases proved to be keratin negative.