http://www.sciencemag.org/news/2020/08/doctors-diagnose-advanced-cancer-dinosaur

This deformed bone is the first clear example of a malignant tumor diagnosed in a dinosaur. The partial fibula—a bone from the lower leg—belonged to a horned, plant-eating Centrosaurus that lived roughly 76 million years ago in what is now Dinosaur Park in southern Alberta in Canada.

Paleontologists initially thought the bone’s strange shape was due to a fracture that hadn’t healed cleanly. But a new study, published today in The Lancet Oncology, compares the internal structure of the fossil (above) with a bone tumor from a human patient to seek a diagnosis. The conclusion: The dinosaur suffered from osteosarcoma, a cancer that, in humans, primarily attacks teens and young adults. The disease causes tumors of immature bone tissue, frequently in the long bones of the leg.