We hypothesized that F. nucleatum might promote colorectal tumorigenesis because 1) F. nucleatum disturbs the intestinal microbiota balance via an increase in opportunistic pathogens and decreased probiotics; and 2) F. nucleatum induces tumor-related immune cytokine secretion, such as IL-21/22/31 and CD40L, and activates the JAK/STAT and MAPK/ERK pathways, which have been reported to promote tumorigenesis. Here, IL21 is linked to neoplasm.