Tumour Microbiome-Based Subtypes of Colorectal Cancer Correlate with Clinical Variables

Abstract BackgroundLong-term dysbiosis of the gut microbiome has a significant impact on the development, progression and the aggressiveness of colorectal cancer (CRC) and may explain part of the observed heterogeneity of the disease from phenotypic, prognostic and response to treatment perspectives. Although the shifts in gut microbiome in the normal-adenoma-carcinoma sequence have been described, the landscape of microbiome within CRC and its associations with clinical variables remain under-explored. ResultsWe performed 16S rRNA gene sequencing of paired tumour tissue, adjacent visually-normal mucosa and stool swabs of N=186 patients with stage 0-IV CRC to describe the tumour microbiome and its association with clinical variable and to derive tumour microbial subtypes.We identified new genera never previously associated with CRC tumour mucosa (Flavonifractor, Haemophilus, Howardella, Pseudomonas, Sutterella, Treponema 2) or CRC (Actinobacillus, Aggregatibacter, Bergeyella, Phocaeiola, Defluviitaleaceae UCG-011, Massilia, Tyzzerella 4). The bacteria residing on tumour-mucosa were dominated by genera belonging to (potential) oral pathogens. Based on tumour microbial profiles, we stratified CRC patients into three subtypes. The subtypes were significantly associated with prognostic factors such as tumor grade, primary tumour sidedness and TNM staging, with one subtype enriched in tumours with poor prognosis. Further, we inspected the associations of microbiome with clinical variables in a subtype-agnostic setting. The primary tumour-associated clinical variables predominantly correlated with tumour mucosal microbiome, while the presence of local and distant metastases was mostly associated with the stool microbiome.ConclusionsUnderstanding the interactions of the bacteria residing on tumour mucosa within different CRC tumour microbiome subtypes will help to better understand the underlying biological background of the heterogeneity of this disease. Indeed, the tumour microbiome is a possible source of additional integrative markers of CRC patients’ survival and prognosis. We found that CRC microbiome is strongly correlated with clinical variables, but these associations are dependent on the microbial environment (tumour mucosa, normal mucosa, stool). Our study thus identifies limitations of the usage of microbiome composition as marker of CRC progression, suggesting the need of combining several sampling sites (e.g. stool and tumour swabs).