DIPG-36. The brain-gut-microbiota axis to predict outcome in pediatric diffuse intrinsic pontine glioma

OBJECTIVE: Diffuse intrinsic pontine glioma (DIPG) is a rare childhood brain tumour with poor prognosis. Radiotherapy (RT) remains the only palliative intervention. In this scenario, it is essential to investigate tumor and patient microinvironment. Microbiota plays a critical role in human health and a functional link between the central nervous system and gut microbiota has been reported: the microbiota-gut-brain axis. With these premises, we have investigated the gut microbiota in DIPG. METHODS: A cohort of 18 patients was enrolled and we collected stool specimens at diagnosis (pre-RT) and after radiotherapy. Microbiota content was analysed through 16S rRNA sequencing on IONS5xl; base calling and demultiplexing were performed by Torrent Suite (ThermoFisher). Association to progression free survival (PFS) and overall survival (OS) were assessed by cox-regression univariate analyses and differential abundance (DA) analyses identified differences following RT. RESULTS: The Firmicutes/Bacteroidetes (F/B) ratio in pre-RT specimens has a median of 0.757 (range= 0.243-1.19). Having PFS as endpoint and at family classification level, an increased risk of disease progression was disclosed for Flavobacteriaceae and Bacillales with HR of 1.57 (p=0.00913) and 1.57 (p=0.215), respectively. The anaerobic bacteria Synergistaceae is found related to a decreased risk of progression with HR 0.662 (p=0.00718). These findings were also confirmed with OS as endpoint. DA analyses pointed out a number of families belonging to Firmicutes and Bacteroidetes phyla highly differentiated (log2|fold-change|>2) between pre- and post-RT. CONCLUSIONS: This study represents the first report of the microbiota-gut-brain axis role in DIPG patients. The F/B ratio, a parameter of normal intestinal homeostasis, show the presence of inflammatory patterns and some family members are associated to increased disease progression. These preliminary findings needs further validations. However, 16S microbiota has the potential ability to stratify patients and probiotic administration could restore a normal F/B ratio.