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Our results identified immune dynamic changes during CRT, indicating that CRT may be immune activating at the site of the tumor. This study also suggests the importance of sequential analyses of the local tumor microenvironment in addition to peripheral blood.

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Purpose: To describe the baseline and serial tumor microbiome in HPV-associated oropharynx cancer (OPC) over the course of radiotherapy (RT). Methods: Patients with newly diagnosed HPV-associated OPC treated with definitive radiotherapy +/- concurrent chemotherapy were enrolled in this prospective study. Using 16S rRNA gene sequencing, dynamic changes in tumor microbiome during RT were investigated. Surface tumor samples were obtained before RT and at week 1, 3 and 5 of RT. Radiological primary tumor response at mid-treatment was categorized as complete (CR) or partial (PR). Results: Ten patients were enrolled. Mean age was 63 years (range: 51-71). As per AJCC 8th Ed, 50%, 20% and 30% of patients had stage I, II and III, respectively. At 4-weeks, 7 patients had CR and 3 patients had PR; at follow-up imaging post treatment, all patients had CR. Baseline diversity of tumoral and buccal microbiomes was not statistically different. For the entire cohort, alpha diversity was significantly decreased over the course of treatment (p=0.02). There was a significant alteration in the bacterial community within the first week of radiation. Baseline tumor alpha diversity of patients with CR was significantly higher than those with PR (p=0.03). While patients with CR had significant reduction in diversity over the course of radiation (p=0.02), the diversity remained unchanged in patients with PR. Patients with history of smoking had significantly increased abundance of Granulicatella (p=0.04), and Kingella (0.05) and lower abundance of Alloprevotella (p=0.04) compared to never smokers. Conclusions: The tumor microbiome of HPV-associated OPC exhibits reduced alpha diversity and altered taxa abundance over the course of radiotherapy. The baseline bacterial profiles of smokers vs. non-smokers were inherently different. Baseline tumor alpha diversity of patients with CR was higher than patients with PR, suggesting that the microbiome as a biomarker of radiation response deserves further investigation.

No abstract