A group of Canadian researchers say they have discovered the first confirmed case of a dinosaur with malignant cancer—by combining the skills used to analyze prehistoric fossils with modern methods used to diagnose humans.

In a study published Monday in the medical journal The Lancet Oncology, researchers led by Toronto's Royal Ontario Museum (ROM) and McMaster University in Hamilton, Ontario, said the case suggested that malignant tumors, including bone cancers, "are rooted quite deeply in the evolutionary history of organisms."

The researchers examined a lower leg bone from centrosaurus apertus, a horned dinosaur that lived 76 to 77 million years ago. The bone itself was originally discovered in 1989 in the badlands of Dinosaur Provincial Park in southern Alberta, Canada, a UNESCO world heritage site and one of the most dinosaur fossil-rich regions in the world.

The bone, which was visibly malformed, caught the eye of researchers on a trip to Alberta's Royal Tyrrell Museum in 2017. A team of experts across both dinosaur and human pathology was assembled, including orthopedic surgeons.

The researchers examined and cast the bone, performed high-resolution CT scans, and sliced the bone into extremely thin sections, examining it at a cellular level to track the progression of the cancer into the bone, before diagnosing the dinosaur with osteosarcoma. The bone was then compared to a regular fibula bone from the same species of dinosaur, and a human bone with a confirmed case of the same cancer.

Osteosarcoma is the most common form of bone cancer in humans, and is usually found in teenagers and young adults, including the Canadian runner Terry Fox.

In the paper, researchers noted that it has previously been difficult to establish evidence of cancer in dinosaur fossils, not only because soft tissue is lost as the bones fossilize, but because the bones are often damaged in the process. The rarity and uniqueness of dinosaur bones has also made researchers reluctant to destroy them in order to conduct tests, they added.

"Diagnosis of aggressive cancer like this in dinosaurs has been elusive and requires medical expertise and multiple levels of analysis to properly identify," said Dr. Mark Crowther, a professor of pathology and molecular medicine at McMaster University, who is also an avowed fan of dinosaurs and a volunteer at the ROM.

"Here, we show the unmistakable signature of advanced bone cancer in a 76 million-year-old horned dinosaur—the first of its kind. It's very exciting."

The dinosaur's cancer was both aggressive and advanced, said Dr. David Evans, a paleontologist at the ROM, and "would have had crippling effects on the individual and made it very vulnerable to the formidable tyrannosaur predators of the time."

He speculated that the large, plant-eating centrosaurus apertus may have been protected by its place in a large, protective herd, allowing it to survive much longer than it normally would have with such a disease.

In the end, researchers concluded that it was unlikely the cancer—or a tyrannosaurus—actually killed the dinosaur.

Instead, its discovery in a massive bone bed alongside other fossils suggested the dino was killed alongside a large herd by another persistent danger: a flood.