Preclinical studies have shown that the response of solid tumors and normal tissues to radiotherapy can be regulated by gut microbiota and its metabolites. In this study, the composition of gut microbiota in patients with locally advanced head and neck cancers undergoing definitive radiotherapy will be analysed together with bacterial metabolites in stool and blood and a possible correlation with treatment outcome and treatment toxicity will be determined.

Head and neck cancer patients commonly present with unresectable locoregionally advanced disease in which radiotherapy is the mainstay of curative-intent treatment albeit at the cost of substantial acute and late toxicity. Recently discovered mechanisms by which gut microbiota and its metabolites impact tumor's and normal tissue's response to radiotherapy offer new ways to improve the therapeutic index of radiotherapy in solid tumors.

COMRAD-HNSCC is a prospective study assessing the correlation between gut microbiota composition and its metabolites and the response to radiotherapy in patients with unresectable locoregionally advanced head and neck cancer. Stool and serum samples will be collected at the beginning and at the end of curative radiotherapy treatment. The composition of gut microbiota will be analysed by ribosomal DNA high-throughput amplicon sequencing of the DNA isolated from stool samples, whereas targeted metabolomics using liquid chromatography-mass spectrometry will be performed on stool and serum samples.

The long-term goal of this study is to deepen the understanding of the role of gut microbiome and its metabolites in efficacy and toxicity of radiotherapy in head and neck cancer, and provide a basis for subsequent exploration to increase therapeutic index by regulating gut microbiota.

Inclusion Criteria:

• Signed written and voluntary informed consent.
• Patient must be willing and able to provide collection for stool specimen analyses at 2 time points.
• Age > 18 years, male or female.
• Patient must be diagnosed with histologically confirmed squamous cell carcinoma of the head and neck (oral cavity, oropharynx, larynx, hypopharynx, or nasopharynx).
• Patients must be eligible for curative-intent treatment with either radiotherapy or concurrent chemo-radiotherapy.
• Overall disease stage III-IV based on 8th edition of American Joint Committee on Cancer staging system.

Exclusion Criteria:

• Receipt of induction chemotherapy.
• Presence of distant metastases.
• Any previous head and neck cancer.
• Any other known concurrent malignant disease.
• Any condition that, in the opinion of the Investigator, would interfere with patient safety, or evaluation of the collected specimen and interpretation of study result.

Adult subjects diagnosed with locoregionally-advanced head and neck squamous cell carcinoma being treated with definitive radiotherapy with or without concurrent chemotherapy at the Institute of Oncology Ljubljana.