Osteosarcoma is a kind of cancer that causes immature bone to form, often on the ends of long bones such as the femur, and has an incidence of 3.4 cases per million people per year. It is more common in the second decade of life, due to the high rate of bone growth during puberty. The genetic cause and related events of osteosarcoma are poorly understood, such that therapies informed by genetics are limited.
Paleopathology, or the study of diseases in ancient human or animal remains, is limited in dinosaurs because often, only their bones are fossilized and/or there is frequent damage that occurred after the dinosaurs died. Diagnosis has also been limited by a hesitation to destroy dinosaur bones to create diagnostic samples, because they are so rare and nique. Clear diagnosis of cancer in dinosaurs has been rare; there have only been a few cases of cancer diagnosed in dinosaurs, but they were diagnosed only using X-ray and examining physical characteristics rather than confirmed through biopsy.
In this report, the researchers found the first confirmed case of osteosarcoma in a dinosaur, in a fossil of Centrosaurus apertus which was an herbivorous horned dinosaur found in Canada that lived approximately 77-75.5 million years ago. The researchers confirmed this diagnosis through examining physical characteristics, using radiological techniques such as X-ray, and histological techniques such as biopsy. The diagnosis was confirmed by experts in oncology and pathology, and also by comparing the diagnosis to a confirmed case of osteosarcoma in humans as well as a normal, cancer-free Centrosaurus fibula. Although birds and reptiles, which descended from dinosaurs, are only distantly related to humans, this comparison may be of high value due to advanced diagnostics and highly specialized expertise that exists for humans.
The cancerous and non-cancerous fibulae were collected from a group of Centrosaurus fossils found in Dinosaur Park and Oldman formations, respectively, both which are located in southern Alberta, Canada. Images of the dinosaur bones can be found in the figure. The human fibula was collected from an above-knee amputation of a 19-year old male with osteosarcoma.
Upon examining the human fibula, the researchers found a tumor inside the central cavity of the bone. X-ray, MRI, and CT examinations showed a Codman’s triangle, which is a new area of bone often caused by a tumor. The tumor was consistent with other human osteosarcomas in that the tumor had not fully become bone, and rather the tumor was made up of small, circular masses of bone and soft tissue. Examination using a microscope showed the formation of immature bone.
The tumor found in the Centrosaurus fibula is a rare case. The researchers found a large abnormality in the fibula towards the pelvic bone. Examination of physical characteristics and tissues as well as assessment by X-ray, MRI, and CT confirmed osteosarcoma, with the same amount of confidence if the tumor was diagnosed in a human. Physical examination of the fibula showed a mass that takes up half of the fibula close to the pelvis, which had a bone covering that was thinner in some areas and multiple large holes. An X-ray CT scan showed a Codman triangle, similar to the human sample, and disruptions in the bone that were similar to high-grade osteosarcomas in humans. It also showed abnormal immature bone formation. Examination of the tissue showed that the tumor extends throughout the bone.
Overall, examinations of the Centrosaurus tumor were consistent and similar to the human specimen, despite the lack of preserved soft tissue in the dinosaur bone. Other diagnoses, including fracture, osteomyelitis, fibroma, and osteochondroma, were rejected. So, the researchers’ findings indicate the presence of osteosarcoma with confirmation from physical, radiological, and histological examination. The extensive invasion of the tumor suggests that the tumor was malignant and may have invaded other organ systems.
In conclusion, in this report the researchers found the first confirmed case of malignant osteosarcoma in a dinosaur. The findings highlight that diagnosing cancer in fossils makes multiple kinds of diagnosis, including physical, radiological, and histological examinations, necessary. The researchers hope that this multifaceted approach allows further diagnoses of other illnesses and injuries in other species. These findings also suggest that illness, such as bone cancers, are deeply rooted in the evolutionary histories of organisms we see today.