LAUSR

Simple Summary The gut microbiota has been suggested to affect tumour development and progression in colorectal cancer. In this study, we investigated the associations of two colorectal cancer-related bacteria, Parvimonas micra and Fusobacterium nucleatum, with survival in colorectal cancer patients. Our results suggest that patients with high tumoural levels of Parvimonas micra have decreased survival. In addition, we found associations for Parvimonas micra and Fusobacterium nucleatum with different clinicopathological and tumour molecular traits. A better understanding of the role of the gut microbiota in colorectal cancer may contribute to improved cancer care. Abstract Increasing evidence suggests that the gut microbiota may impact colorectal cancer (CRC) development and progression. In this study, the tumour colonisation of two CRC-associated bacteria, Parvimonas micra and Fusobacterium nucleatum, was studied in relation to patient survival in a cohort of 257 CRC patients. Colonisation of P. micra and F. nucleatum was analysed in fresh frozen tumour tissue (n = 112) and in faeces (n = 250) by qPCR. When analysing tumour tissues, both P. micra and F. nucleatum were found to be associated with decreased five-year cancer-specific survival, an association that remained significant in multivariable analysis for P. micra. Furthermore, we found significant associations of high levels of P. micra and F. nucleatum with tumour molecular characteristics, i.e., tumours mutated in BRAFV600E, and tumours of the MSI subtype. The analysis of faecal samples showed weaker associations with prognosis and tumour molecular characteristics. In conclusion, our findings support a novel association of tumour colonisation of P. micra with decreased patient survival. A better understanding of the role of the gut microbiota in CRC might contribute to the advancement of prognostic tools and new targets for therapy.