So many dinosaur bones show evidence of having been affected by tumors, it suggests bone cancer was an occupational hazard in the Cretaceous. However, we've had only unreliable hints that any of these were able to spread to other parts of the body. Now, however, the first malignant cancer has been detected in a dinosaur bone, even if it's not much use to the victim.

The capacity of malignant cancers to spread to other organs makes them serious concerns. However, we can't biopsy dinosaur tumors for the DNA, so it's not easy to tell if a fossilized tumor had this potential, although a similarly ancient turtle tumor has been diagnosed this way.

When a fibula from a Centrosaurus apertus was found in 1989 in Dinosaur Provincial Park, Alberta, it was not even recognized as hosting a cancer. Instead, its malformation was attributed to a partially healed fracture. However, on visiting the Royal Tyrrell Museum in 2017, Dr David Evans of the Royal Ontario Museum saw the leg bone and thought it deserved further investigation.

Evans drew together a team of scientists from a range of fields to use modern medical technology to assess what they had found.

Using high-resolution CT scans to image the tumor's individual cells, the team compared what they saw to images of osteosarcoma in a bone from a 19-year-old whose leg had been amputated. Osteosarcoma is a malignant bone cancer that affects about 1,000 Americans a year, particularly teenagers. After considering three alternative explanations, the team concluded the dinosaur had the same condition. Having your cancer matched to a dinosaur's isn't much compensation for losing a limb, but it has a certain coolness factor.

“The extensive invasion of the cancer throughout the bone suggests that it persisted for a substantial period of the animal’s life and might have invaded other body systems,” the authors report in The Lancet Oncology. “A similarly advanced osteosarcoma in a human patient, left untreated, would certainly be fatal.”

Nevertheless, it almost certainly was not cancer that killed the poor C. apertus, at least not directly. The site where the bone was found is littered with others of the same species, suggesting a herd of these sociable horned herbivores were all felled by the same phenomenon, probably a flash flood.

Having such a weakened bone presumably hindered this individual's chances of escaping the torrent, even if the cancer was not widespread through its body, but plenty of healthy others met the same fate.

The discovery may tell us something about Centosaurus' behavior. Evans notes a partially crippled individual like this would have been vulnerable to tyrannosaurs. "The fact that this plant-eating dinosaur lived in a large, protective herd may have allowed it to survive longer than it normally would have with such a devastating disease,” he said in a statement.

Osteosarcomas tend to strike when bones are growing rapidly, something presumably hard to avoid when you weigh three tonnes.