ACVIM Small Animal Internal Medicine (SAIM) Seminal Paper Practice Exam

The key idea here is that finding Fusobacterium spp. more often in cats with GI lymphoma does not prove it causes the cancer. In feline GI lymphoma, associations between Fusobacterium and the disease have been observed in some studies, but there is no solid proof that these bacteria initiate or drive the lymphoma. It’s equally plausible that the cancer changes the gut environment in ways that favor Fusobacterium growth, or that both the bacteria and the tumor arise from shared risk factors such as diet, antibiotic exposure, or immune status.

To establish causality, we’d need evidence showing that Fusobacterium enrichment precedes lymphoma development and that actively altering Fusobacterium levels changes tumor risk or progression, ideally with longitudinal data and mechanistic experiments. While there’s plausible biology supporting a causal role in other species or contexts (inflammatory cascades, immune modulation, and potential genotoxic effects), the current feline data do not demonstrate causality. So the accepted stance is that causality has not been established and the relationship could be either a consequence of the disease or a contributing factor.