Evaluation of primary tumor and metastasis microbiome in HNSCC

Introduction Local bacterial contribution to the development of HNSCC has received increasing attention over the past few years. This study aims to investigate bacterial involvement in metastasis as a promising approach to better understand the tumor microenvironment as well as the process of metastasis.

Methods Tissue samples from 24 patients with HNSCC were collected prospectively. The local ethics committee approved the study, and all patients gave informed prior consent. Qualitative microbiome analysis was performed by amplifying and sequencing the V3-V4 region of the 16S gene with the Illumina MiSeq system. Bioinformatical analysis of the sequencing data was performed with IMNGS2, Rhea and namco. Quantitative analysis of bacterial load was performed using real-time qPCR targeting the V3 region of the 16S gene.

Results Quantitative PCR showed a significant difference between the bacterial load of the lymph node metastasis and that of the negative controls for contamination. In the qualitative analysis of the bacterial signatures with 16S sequencing, mainly bacteria of the strains Proteobacteria and Firmicutes were found in the tumor samples. In the individual comparison of primary tumor and metastasis of the same patient, it can be determined that bacterial strains found in the metastasis are also predominantly found in the primary tumor.

Conclusion Bacteria are present in lymph node metastasis of HNSCC. However, primary tumor and metastasis differ in their beta diversity. A possible explanation for this would be a shift of the microbiome due to differences in the microenvironment. To answer the question to what extent bacteria affect the tumor microenvironment and metastasis, further investigations are needed.

Funding information Funded by the "Dr Helmut Legerlotz-Stiftung", the Faculty of Medicine of the Technical University of Munich and the SFB1371 Microbiome Signatures (DFG)