P04.25 MOLECULAR ANALYSIS OF STEREOTACTIC BIOPSIES COMPARED TO TISSUE SAMPLES FROM OPEN TUMOR RESECTIONS IN GLIOMAS

Biomarkers, genetic alterations and epigenetic marks gain in importance as prognostic and predictive markers both, after primary diagnosis and in the recurrent disease situation. However, tissue samples are needed throughout the longitudinal course of the disease in order to adjust therapy to changing conditions. A remaining question is whether an open tumor resection is superior for pathological and molecular analysis compared to a small stereotactic biopsy. We compared the diagnostic potential of stereotactic biopsies to tissue samples from gross total resections. 16 stereotactic 1-mm tissue samples (2 diffuse astrocytomas, 2 anaplastic astrocytomas, 9 glioblastomas, 3 other tumors) were analyzed with an approach combining histopathologic diagnosis with small sample size-adjusted moleculargenetic analysis. Serial biopsies were taken throughout the tumor. Single probes were taken for single analysis (e.g. 1 probe for immunohistochemistry, 1 probe for genomic DNA extraction, 1 probe for RNA and protein extraction etc.). This procedure is eligible as the literature reports homogeneous distribution of biomarkers throughout tumors. We report that for each single patient a microscopic analysis, different immunhistochemical stainings (e.g. GFAP, S100, Vimentin, MAP2, EGFR, IDH1, p53, and MIB-1) as well as biochemical and molecular analysis could be performed with material obtained from a single stereotactic biopsy. The biochemical analysis was done by Western blot using various antibodies (e.g. ALDH1, AHR, GFAP, beta-actin). Furthermore, molecular techniques were applied including the methylation status of the MGMT promoter by bisulfit conversion of the DNA and following PCR and the IDH1/2 mutation status verification by pyro-sequencing. Genomic DNA could be extracted from all stereotactic probes. RNA extraction was also possible, but the amount of cDNA which could be obtained from the RNA of stereotactic samples was significant lower in 14 (out of the 16) samples than the amount of cDNA normally used for quantitative RT-PCR from open operations. There was no biopsy-related morbidity. We conclude that determination of many different immunohistochemical, biochemical, and molecular parameters are possible using the stereotactic biopsy technique. Moreover, the procedure is safe and reliable. The stereotactic biopsy enables decision making for optimizing the treatment of brain tumors without the necessity of an open resection. This finding has even more clinical im