In humans, which bacterium is linked to an increased risk for colorectal cancer, pancreatic cancer, and oral squamous cell carcinoma?

• A. Fusobacterium nucleatum
• B. Escherichia coli
• C. Streptococcus mutans
• D. Helicobacter pylori

Answer: (A)

A bacterium that can promote cancer across multiple sites often does so by directly interacting with host cells and shaping a pro-tumor inflammatory environment. Fusobacterium nucleatum fits this pattern and has been repeatedly linked to colorectal cancer, pancreatic cancer, and oral squamous cell carcinoma.

Its key trick is directly touching epithelial cells and altering signaling. The FadA adhesin allows F. nucleatum to bind to E-cadherin on epithelial cells, which releases and activates β-catenin signaling. This drives transcription of genes that promote cell proliferation and survival. At the same time, the bacterium engages Toll-like receptor 4 pathways, fueling inflammation and shaping a tumor-promoting microenvironment. This combination of enhanced cell growth, immune modulation, and inflammatory signaling helps cancer develop and progress, and the bacterium is found enriched in tumor tissues and even detectable in saliva, linking it to cancers in the colon, pancreas, and oral cavity.

Escherichia coli can be associated with colorectal cancer in some contexts (notably certain genotoxic strains), but its strongest and most consistent links aren’t across all three sites mentioned. Streptococcus mutans is central to dental caries and has been investigated for oral cancers but is not a well-established link to pancreatic or colorectal cancer. Helicobacter pylori is best known for gastric cancer risk, not colorectal or oral squamous cell carcinoma.