CIRCULATING CELL-FREE DNA AS PROGNOSTIC AND MOLECULAR BIOMARKER FOR PATIENTS WITH GLIOBLASTOMA UNDER INHALED PERILLYL ALCOHOL TREATMENT

Anabolic, infiltrative and diffuse nature of glioblastoma (GBM) impairs complete surgical resection favouring tumor recurrence due to radio and chemoresistance and oncogenic metabolic reprogramming. Despite recent advances on brain imaging, up to now there is no diagnostic tool capable to detect incipient tumor niches and differentiate from inflammatory infiltrate/ radionecrosis. Intranasal administration of perillyl alcohol (POH) is a novel adjuvant therapy known to increase survival of patients with recurrent GBM (rGBM). Patients with cancer present high levels of circulating cell-free DNA (cfDNA) as result of intense tumor activity (necrosis and apoptosis), thus providing a noninvasive screening tool for early tumor recurrence prior to image detection. We aimed to verify the potential of cfDNA as a biomarker to differentiate cancer patients from healthy subjects and monitor patients response to POH therapy. The cohort included 130 healthy subjects as control-paired group and 56 rGBM patients at terminal stage enrolled in POH trial (CONEP 9681/ 25000.009267/2004-25). rGBM patients response to POH therapy were evaluated based on cfDNA quantification and magnetic resonance image (MRI). Mean cfDNA levels of rGBM patients were 29.5-fold increased (1,179.7 ng/mL) compared to healthy subjects (40 ng/mL). Receiver operating characteristics (ROC) analysis revealed good degree of sensibility and specificity of cfDNA in discriminating patients from controls (area under the curve, AUC = 0.994). It was observed a significant (p = 0.034) difference on cfDNA levels considering mean survival time of 72 weeks. Hence mean cfDNA levels were highly augmented (1.546,7ng/mL) for those patients with lower survival (mean: 26.31 weeks) compared to patients with longer survival (mean:167 weeks; cfDNA = 465 ng/mL), with a weak, significant and negative correlation between these variables (p = 0.031, rho = -0.288). Log-rank analysis (Kaplan Meier) showed significant differences regarding probabilities of survival for both patient groups (p < 0.0001). Maintenance of low cfDNA levels and MRI pattern of complete response was consistently observed for those patients with longer survival (higher than 6 years) under of POH therapy. However, therapy discontinuation caused a 2.35-fold increase of cfDNA levels and MRI compatible with tumor recurrence. Such findings point cfDNA as a non-invasive method to early detect tumor recurrence and monitor rGBM response to therapy.