ESTRO 2024 - Abstract Book

S799

Clinical - CNS

ESTRO 2024

891

Poster Discussion

Antibiotic exposure during treatment with radiotherapy for glioblastoma impacts survival.

Sean Main 1,2,3 , Omar Al-Salihi 1 , Angela Swampillai 1 , Lucy Brazil 1 , Kazumi Chia 1 , Vishal Manik 1 , Miguel Reis Ferreira 1,4

1 Guy's and St Thomas' Hospital NHS trust, Guy's Cancer Centre, London, United Kingdom. 2 Tessa Jowell Brain Cancer Mission, Tessa Jowell Brain Cancer Mission Fellow, London, United Kingdom. 3 University Hospital Southampton, Department of Clinical Oncology, Southampton, United Kingdom. 4 King's College London, Centre for Host Microbiome Interactions, London, United Kingdom

Purpose/Objective:

Glioblastoma multiforme is a very aggressive brain tumour. Despite treatment with radiotherapy (with or without chemotherapy), which can be preceded by surgery; survival outcomes are poor and only about 25% of patients survive for 12 months or more. Factors such as methylation of the MGMT gene promoter, use of chemotherapy and greater extent of resection are associated with a better prognosis. The impact of the microbiota is under-researched in neuro-oncology compared to other cancer sites. In other cancers, evidence suggests reduced efficacy of anti-cancer treatments in patients who have been exposed to antibiotic therapies, suggesting an impact of the human microbiome on treatment outcomes. Possible mechanisms for this effect include antibiotic alterations in gut microbiota composition or direct effects on tumour microbiome. These relationships have never been assessed in neuro-oncology. In this study we addressed this gap in knowledge by assessing the impact of antibiotic uptake on post-treatment survival in a cohort of patients treated with radiotherapy for glioblastoma multiforme (GBM).

Material/Methods:

We conducted a retrospective study on a cohort of patients treated at a high-volume tertiary centre in the UK. Data was collected from electronic patient record systems. Antibiotics used peri-operatively and as Pneumocystis pneumonia prophylaxis were excluded. Patients received radiotherapy with either 60Gy/30 fractions or 40Gy/15 fractions. Radiotherapy was either adjuvant or definitive. Chemotherapy with concurrent and/or adjuvant temozolamide was used as per national guidelines. The cohort was characterised by distribution measures. Overall survival (OS) and disease-specific survival (DSS) rates were assessed with Kaplan-Meier models. Multivariate Cox proportional hazard regression was used to assess the validity of associations while adjusting for confounders. Variables included were: antibiotic exposure, performance status, methylation status, PS at presentation, radiation dose and use of concurrent chemotherapy.

Results:

Between 2016-2021, 252 patients were treated and included for analysis. MGMT promoter methylation was detected in 103 (40.87%) patients. Concurrent chemo-radiotherapy (STUPP regimen) was delivered to 171 (67.86%)