No pet lover wants to hear this, but around 6 million dogs are diagnosed with cancer in the US every year. Cancer is, heartbreakingly, the main reason dogs die. But don't despair: scientists are working on it.
A new study suggests certain types of bacteria in the gut microbiomes of dogs with cancer are somehow linked to how long these dogs survive after immunotherapy treatment.
"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 explain in their published paper.
Could the same be true for dogs?
Fifty-one canine cancer patients at the Bridge Animal Referral Center in the US were enrolled for a clinical trial of a cancer immunotherapy vaccine that has already shown a lot of promise.
This vaccine helps the immune system fight tumor growth by inhibiting two proteins, EGFR and HER2, that are overexpressed in some cancers. The hope is the vaccine will give dogs with cancer a bit more quality time with their loved ones, if not a full recovery.
But a dog's immune response does not occur in a vacuum; it acts in a bustling city of microbes with their own agendas. As decades of research have shown, the bacteria, fungi, and other microbes that live in the intestinal tract affect an animal's immune response in the gut itself and throughout the body.
Analyzing rectal swabs from the dogs at Bridge, and following up on the dogs' survival outcomes after treatment, the researchers identified 11 kinds of bacteria that appear to affect the vaccine's success.
Four of these bacteria were associated with a longer survival time after treatment; seven were linked with shorter survival. These relationships held up regardless of the dog's breed or cancer type.
That suggests a dog's gut bacteria could be modulating its immune responses, even against non-intestinal cancers such as osteosarcoma (a kind of bone cancer) or hemangiosarcoma (cancer of the blood vessels).
The study didn't explore the mechanisms of how these bacteria might actually affect outcomes one way or the other – that's something for 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, who studies host-microbiota interactions at Oregon State University.
It's very early stages for this research and for the immunotherapy treatment in general, but the findings hint that microbial treatments such as probiotics or fecal transplants could supplement the canine cancer vaccine.
Related: Breakthrough Cancer Vaccine For Dogs Is 'Truly Revolutionary', Scientist Says
"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.