Characterization of candidate tissue and blood biomarkers in a rare cohort of myxopapillary ependymoma patients.

Abstract

2040 Background: Myxopapillary ependymoma (MPE) is a very rare tumor of the distal spinal cord. Despite benign histopathology, local recurrences occur in approximately 30% of patients and distant metastases have been described in few cases. We investigated candidate tissue and blood biomarkers in a rare MPE series. Methods: Formalin fixed paraffin embedded (FFPE) tumour tissues from 21 MPE patients were immunohistochemically investigated for expression of isocitrate dehydrogenase 1 R132H (IDH-R132H), Secretagogin, glial fibrillary acidic protein (GFAP), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), estrogen receptor (ER), Ki-67, arg, plateled derived growth factor a (PDGFRa) and b (PDGFRb), pc-kit and pc-abl. EGFR gene was evaluated using exon-sequencing. In addition, we analyzed circulating plasma-GFAP using ELISA in 3 patients with completely resected MPE, 1 patient with locally advanced MPE, 2 patients with pleuropulmonary metastases of MPE and 12 control subjects. Results: Secretagogin and GFAP were expressed in all tissue samples. arg, PDGFRa, PDGFRb, pc-kit and pc-abl were positive in 15, 1, 2, 3 and 2 patients, respectively. The Ki-67 index ranged from 1% to 12.8% (median=7.1%). We detected no expression of EGFR, IDH-R132H, HER2, PR or ER. One patient showed a silent mutation in exon 21 of the EGFR gene (c.2508C>T). We found very high concentrations of plasma-GFAP in two MPE patients with pleuropulmonary metastases, while all other MPE patients were negative. Conclusions: Our data indicate that (i) targeted tyrosine kinase inhibitors may be rational for the therapy of selected MPE patients and that (ii) circulating GFAP could be useful as circulating marker for the early detection or follow-up of distant metastases in MPE patients.