Dog Gut Microbiome May Influence Cancer Immunotherapy Survival

No pet owner wants to face this reality, yet about 6 million dogs in the US receive a cancer diagnosis each year. Tragically, cancer is the leading cause of death in dogs. Even so, researchers are pursuing new ways to tackle it.

New research indicates that particular bacteria in the gut microbiomes of dogs with cancer may be connected to how long they live following immunotherapy.

"Studies in humans have linked specific gut microbiome signatures to clinical outcomes in cancer patients receiving immunotherapy, highlighting their potential as diagnostic or prognostic biomarkers," the researchers write in their published paper.

Could this also apply to dogs?

Canine cancer immunotherapy vaccine trial

A clinical trial enrolled 51 dogs with cancer at the Bridge Animal Referral Center in the US to test a cancer immunotherapy vaccine that has already demonstrated considerable promise.

The vaccine supports the immune system in combating tumour growth by blocking two proteins, EGFR and HER2, which are overexpressed in certain cancers. The aim is to offer dogs with cancer more quality time with their families, even where a complete recovery is not possible.

However, a dog's immune system does not operate alone. It functions within a busy community of microbes, each with its own role. Decades of studies have established that the bacteria, fungi and other microbes inhabiting the intestinal tract can influence an animal's immune response, both in the gut and elsewhere in the body.

Gut microbiome bacteria and dogs' cancer survival

The researchers examined rectal swabs collected from the Bridge dogs, then tracked their survival after treatment. They found 11 bacterial types that seem to influence how well the vaccine works.

Four of those bacteria were linked to longer survival after treatment, while seven were associated with shorter survival. The associations remained consistent irrespective of the dog's breed or type of cancer.

This indicates that gut bacteria may shape a dog's immune responses even when the cancer is outside the intestinal system, including osteosarcoma, a form of bone cancer, and haemangiosarcoma, which affects blood vessels.

The study did not investigate the mechanisms through which the bacteria could alter outcomes in either direction. That question will need to be addressed by future research.

"Our study is a first step toward using the gut microbiome as a tool to develop prognoses and to manipulate cancer, not just in dogs, but potentially as a model for human treatments as well," says Natalia Shulzhenko, a researcher in host-microbiota interactions at Oregon State University.

Both this research and the immunotherapy itself remain at a very early stage. Nevertheless, the findings suggest microbial interventions, including probiotics and faecal transplants, could potentially complement the canine cancer vaccine.

"In the future, an analysis of a microbiome swab could help predict how well a dog might respond to a cancer treatment," Shulzhenko says.

"This allows pet owners and vets to make more informed decisions about care. And now that we know certain bacteria are linked to survival, we can explore ways to 'fix' a dog's gut microbiome to help the vaccine work better and help the dog live longer."

The research was published in Veterinary Oncology.