P14.04.B CIRCULATING TUMOR CELLS AS A NON-INVASIVE GLIOBLASTOMA DIAGNOSTIC AND PROGNOSTIC TOOL

Abstract

Abstract BACKGROUND Circulating tumor cells (CTCs) detection in the blood of glioblastoma (GBM) patients can facilitate the assessment of tumoral information without the need for invasive approaches. Our aim is to use GBM CTCs to obtain knowledge about the tumor and improve the current GBM diagnosis and prognosis. MATERIAL AND METHODS We collected primary, matched recurrent GBM and healthy controls blood samples. CTCs were enriched from whole blood controls with Parsortix Cell Separation System and analysed on DEPArray system. CTCs were recognized by immunofluorescence with GFAP.The CTCs have been counted for all the samples. Copy Number Aberrations (CNAs) analysis was performed on CTCs. To compare CTCs genetic background with the same patient’s primary and recurrence tissues, whole exome sequencing (WES) was realized on tumor tissues. Recurrence of GBM was diagnosed according to the RANO criteria +/-path proven second surgery +/- FET PET imaging proven. We assessed tumor volume of contrast enhanced (CE) (as a surrogate marker of BBB damage) and nCE at the time of the CTCs collection by seminautomatic segmentation on ITKsnap software. RESULTS We found CTCs in GBM patients newly diagnosed at the time of first surgery (86%) but also at recurrence (100 %). Cell counting demonstrated in both primary and recurrent GBM patients’ blood a statistically significantly higher number of CTCs compared to healthy controls (average of cells number 15.8 vs 2.3). Interestingly, recurrent GBM patients showed more CTCs than primary GBM patients (average 9 vs 22.7). CNAs analysis confirmed the tumor status of the selected CTCs. Some of GBM classical mutations (in HTERT promoter, BRAF, PTEN, PI3KCA and EGFR genes) have been searched both in the tumor tissues and in the CTCs. HTERT was found mutated in CTCs of one patient’s tumor carrying mutant HTERT and wild type IDH1/2. We also included three IDH1 mutant glioma patients and one BRAFV600E mutant GBM patient in order to track these in CTCs. We did not find BRAF mutations in CTCs isolated from one recurrent BRAFV600E GBM patient with a very low allele frequency in the recurrent tumor (<1%). CONCLUSION We found CTCs in GBM patients newly diagnosed and at recurrence. Several factors may affect CTCs release such as tumor volume, CE and the CTCs genetic BACKGROUND , which seems to be heterogeneous. CTCs detection by our methodology could be helpful in the clinical setting for diagnostic, prognostic and theranostic purposes and for patients monitoring. Prospective study is ongoing in order to assess CTCs variations on and after therapy. This study, first investigated the genetic heterogeneity of CTCs released in the blood flow from the parental tumor.