• Cancer was found in a fibula (lower leg bone) belonging to a Centrosaurus. (Photo: Fred Wierum)

No one can really confirm what killed the dinosaurs. Volcanic eruptions, meteors, and climate change are all common answers to the question. Now there’s a new idea – what about cancer?  

A recent discovery, led by a multidisciplinary team of Canadian researchers has found a type of malignant bone cancer in a dinosaur bone, a type of cancer that continues to affect humans today.

Osteosarcoma is a kind of bone cancer that affects about 3.4 million people per year. In fact, osteosarcoma is the same type of cancer that Canadian athlete, Terry Fox was diagnosed with in 1977. Prior to the study that led to this discovery, no malignant cancers had ever been documented in dinosaurs before.

The study, published in The Lancet, was led by Dr. David Evans, a dinosaur paleontologist at the Royal Ontario Museum, and Dr. Mark Crowther, a professor of pathology and molecular medicine at McMaster University. Together, they began looking for pathologies in fossils that had not been previously identified. To help with diagnosis and examination, a team consisting of engineers, radiologists and imaging scientists were brought in to help with the project.    

“Dr. Crowther and Dr. Evans set out to find anything that occurs in humans, but that also happened in dinosaurs that we hadn’t yet identified,” says Seper Ekhtiari, an orthopaedic surgery resident at McMaster University and co-author of the study. After coming across a bone, which had been previously classified as having a fracture callus (bony material developed during repair) in the Royal Tyrrell Collection in Alberta, Ekhtiari says that Crowther and Evans thought it looked uncharacteristic and examined it further. 

“From there, it was just a matter of coming to a diagnosis,” says Ekhtiari.

The bone cancer was found in belonged to a Centrosaurus. (Photo: Evans, Crowther/The Lancet)

The bone was originally discovered in Alberta’s Dinosaur Provincial Park in 1989 and was a fibula (lower leg bone) belonging to a Centrosaurus. Existing about 75 million years ago during the Cretaceous period, this egg-laying herbivore lived in areas of North America like Alberta, Colorado, and Saskatchewan. With a frill on the top of its head and a single large horn, the Centrosaurus looks similar to the better-known Triceratops.

To diagnose the bone, the same approach taken to diagnose a human was taken on the dinosaur, says Ekhtiari. 

“If someone comes in with a new tumor and we don't know what tumor it is, we would examine the patient beginning with looking at it from the outside.” 

Using medical imaging tests, like X-rays and CT scans, further studies would be made, followed with a biopsy to be examined under a microscope. All of these various findings would then have been compiled into one diagnosis.

Ekhtiari says that this finding can help tell us about the underlying biology of cancer. 
“It certainly teaches us about the evolutionary history of the disease and anytime we can gain a better understanding of any disease, especially cancer,” says Ekhtiari. “It helps us to better understand what causes it, how it forms, and how it progresses.”

In humans, osteosarcoma typically occurs in the second decade of human life, between the ages of 10 and 20. Ekhtiari says that it is thought to be this way because this is when humans are growing the most quickly. 

“It's interesting to find in a dinosaur, because one of the ways they got to their enormous size was by growing extremely rapidly,” says Ekhtiari. “This adds more credence to that theory that there's a relationship between the rate of growth, and the occurrence of osteosarcoma, which is basically just abnormal bone formation.”

The bone was originally discovered in a bone bed, a large collection of bones from the same species but hundreds and thousands of individuals. Generally, this suggests a mass death event. In this case, Ekhtiari says it was most likely from a flood.  

So, was it cancer that killed the dinosaur?

Ekhtiari says it is hard to know for sure because it was still with the herd when it died. 

“Maybe the cancer killed the dinosaur and the flooding happened very shortly after, but that's very speculative and our best guess is that it probably was not the cancer itself.