After a train carrying chemicals derailed and caught fire in East Palestine, Ohio, in 2023, residents were exposed to carcinogens such as vinyl chloride, acrolein and dioxin. Since tumors are typically slow to develop, it could take decades to know what that might have done to the locals’ cancer risk. But there may be a quicker route to an answer: The residents’ dogs were also exposed, and dogs develop cancer more quickly.
Studying dogs and their cancers turns out to be an excellent way to learn more about cancer in people. And it’s not just that dogs and owners share exposures to many of the same environmental carcinogens. Researchers are also learning that cancers develop along remarkably similar pathways in the two species.
The faster pace at which canine cancers progress also means that researchers testing new therapies can get quicker results than with human clinical trials. This benefits scientists, dogs and their owners, proponents say.
“Man’s best friend is man’s best biomedical friend,” says Matthew Breen, a geneticist at North Carolina State University. “It’s like having a mobile BioSentinel organism that can help inform us about our own medical prospects over the next 25 years.”
Dogs in the vanguard
The biomedical bond between people and dogs is not new. Veterinarians have long treated canine patients with drugs developed for use in people, and doctors have relied on dogs to test therapies and procedures before deploying them in the clinic. Techniques to treat the bone cancer osteosarcoma without amputating the patient’s limb, for example, were first developed in dogs.
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Yet today this cross-fertilization is no longer an occasional benefit. Researchers are realizing that canine tumors parallel those in people so closely that dogs may be the best reference point for understanding many human cancers.
One of the most important similarities between canine and human cancers is that they arise after a protracted struggle at the cellular level. Over the years, cells accumulate genetic damage that disables normal controls on cell division, and emerging tumors evolve ways to evade the immune system. So there can be many different pathways to cancer that differ from tumor to tumor — and, it turns out, even from cell to cell within a single tumor.
Traditional lab-mouse approaches to studying cancer miss much of that heterogeneity, because the system is more artificial. Researchers typically have to implant tumors into inbred strains of mice whose immune systems have been suppressed.
But new genetic research underscores how similar the accumulating damage is in dogs and people. In a yet-to-be-published study, Elinor Karlsson, a genomicist at the UMass Chan Medical School, and colleagues looked at genes from more than 15,000 human tumors of 32 different types and more than 400 canine tumors of seven different types.
The aim was to identify genetic mutations present in the cancers but not in normal cells of the same individual. Such mutations were presumably not inherited but probably represented genetic damage accumulated over a lifetime.
That damage looked remarkably similar in the two species, Karlsson says. “Genetically, in terms of what’s driving cancers, it’s basically the same genes in dogs and humans.”
Many of the dog tumors, for example, had mutations in genes already known to drive human cancers, such as the tumor suppressor gene PTEN, often mutated in breast and prostate cancers. Notably, mutations often occurred in or near the same locations in the genes in both species, suggesting that they may cause similar dysfunctions.
A similar recent finding came from researchers at FidoCure, a California-based company where scientists are investigating how tumors with specific mutations respond to human therapies. Records of 1,108 dogs with cancer showed that dogs whose tumors carried particular mutations had higher survival rates if they were treated with a human drug specific to that mutation. This implies that the underlying biology of the cancers may be similar in the two species, and if so, researchers ought to be able to use dogs as a test bed to develop new therapies for people.
That has already paid off in therapies first developed in dogs that are now in clinical trials or approved for use for people, says Amy LeBlanc, a veterinary oncologist and director of the comparative oncology program at the National Cancer Institute. Examples include immunotherapies for brain cancers; viral therapy that targets lymphoma; and drug therapies against multiple myeloma, lymphoma and brain tumors.