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Dogs are the oldest domesticated animal, working alongside humans for thousands of years — so it's no surprise that man's best friend and humans share so many unique qualities.

But the more we learn about our pet companions, the more scientists realize that we are more like our dogs than we know.

"The genetic difference between humans and dogs is quite small," said Dr. Rodney Page, professor of medical oncology and director of the Flint Animal Cancer Center. "Humans and dogs are 95 percent identical genetically — and the diseases that affect humans including breast cancer, prostate cancer, and melanoma are almost identical."

In fact, cancer is so common in dogs that doctors are studying them as a model for treating the disease in humans.

Comparative oncology, a new field that integrates cancers seen in veterinary patients into more general studies of cancer biology and therapy, studies the similarities between naturally occurring cancers in pets and cancers in people — in hopes that our genetic similarities can provide clues to treat cancer more effectively.

Doctors estimate that there are 400 to 500 diseases that are genetically identical between dogs and humans.

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"Over the last five years, there's been a tremendous increase in [comparative oncology] awareness to the extent that the National Cancer Institute has released a significant amount of funding to study cancer in dogs as a way to improve human health," Page said.

What 3,000 golden retrievers can teach us

What scientists have learned from dogs, helped save the life of Emily Brown, 31, who was 11 when doctors told her she had three months to live.

Emily Brown, 31, and her golden retriever who was recently diagnosed with soft tissue sarcoma and is going through her own treatment. NBC News

Bone cancer had spread from her ribs and spine to her lungs.

"It was tough going to bed at night, cause you never know, ‘Am I gonna wake up in the morning," said Brown, who lives in Monument, Colorado.

Doctors told her that her last hope was an experimental drug, but it wasn't created for humans — it was a cancer drug for dogs.

Her immunotherapy treatment, was one of at least four drugs that had made it to human trials after being highly successful at ameliorating cancer in dogs. Colorado State University, which lead the research, is one of 20 major medical centers conducting clinical trials of drugs that could potentially cure cancer in dogs.

CSU scientists are also studying 3,000 golden retrievers, the breed with the highest rate of cancer. The dogs are being followed from birth to death.

“I didn’t even think dogs got cancer.”

"We'll be able to have 3,000 stories about where each dog went, what they ate, where they slept, how they interacted with their owners," Page said. "It's a great opportunity to not only study how to improve their health and wellness, but also to apply these practices to various aspects of human health.”

Brown's survival indicates comparative oncology might be a key to fighting cancer. She has been cancer free for 20 years. Her gratitude for the canine research has strengthened the bond with her own dog, Gertrude.

"The role of animals in our lives has been well-known, as therapy, guide, and service dogs. What we’re doing now provides an opportunity for companion animals to serve as supporters of clinical research in a way that will transcend their other functions," Page said.