Fusobacterium and colorectal cancer: causal factor or passenger? Results from a large colorectal cancer screening study.

Colorectal cancer is a leading cause of morbidity and mortality worldwide in both men and women. The gut microbiome is increasingly recognized as having an important role in human health and disease. Fusobacterium has been identified in former studies as a leading gut bacterium associated with colorectal cancer, but it is still not clear if it plays an oncogenic role. In the current study, fecal samples were collected prior to bowel preparation from participants of screening colonoscopy in the German BliTz study. Using 16S rRNA gene analysis, we examined the presence and relative abundance of Fusobacterium in fecal samples from 500 participants, including 46, 113, 110 and 231 individuals with colorectal cancer, advanced adenomas, non-advanced adenomas and without any neoplasms, respectively. We found that the abundance of Fusobacterium in feces was strongly associated with the presence of colorectal cancer (P-value < 0.0001). This was confirmed by PCR at the species level for Fusobacterium nucleatum. However, no association was seen with the presence of advanced adenomas (P-value = 0.80) or non-advanced adenomas (P-value = 0.80), nor were there any associations observed with dietary or lifestyle habits. Although a causal role cannot be ruled out, our observations, based on fecal microbiome, support the hypothesis that Fusobacterium is a passenger that multiplies in the more favorable conditions caused by the malignant tumor rather than a causal factor in colorectal cancer development.