What causes Canine Osteosarcoma? (National Canine Cancer Foundation)

The exact causes of osteosarcoma are not known. 

• Factors like ionizing radiation, chemical carcinogens, foreign bodies, (including metal implants, like internal fixators, bullets, and bone transplants), and pre-existing skeletal anomalies like the site of healed fractures sometimes lead to osteosarcoma.
• It has also been associated with chronic osteomyelitis and in fractures in which no internal repair was used.
• Osteosarcoma has been concurrently seen in dogs with bone infarcts.
• In dogs, injected with plutonium during experimental studies, the occurrence has been found to be rampant.

What are the genetic factors that can induce osteosarcoma tumor growth?

Genetic factors are also believed to induce the development of tumors.

• Dogs with OSA have been found to have aberrations of the p53 tumor suppressor gene.
• In laboratory animals, both DNA viruses (polyomavirus and SV-40 virus) and RNA viruses (type C retroviruses) have been found to trigger osteosarcoma.
• Alterations in several growth factors like cytokine or hormone signaling systems have been documented in the pathogenesis of the disease.
• Greater blood vessel density has been shown to be an indicator of primary Osteosarcoma with metastasis. (National Canine Cancer Foundation)

Etiology and Risk Factors of Osteosarcoma

AKC Canine Health Foundation

Etiology and Risk Factors of Osteosarcoma (AKC Canine Health Foundation)

A major component of this disease in dogs, and possibly in people, appears to be genetic (i.e., heritable). Risk is most accurately defined by body mass, although there is a direct correlation with size as well. In dogs, there are clear breed predispositions.

Environmental factors that increase risk for osteosarcoma include rapid growth (therefore “large breed” puppy food has reduced levels of available energy to increase the time needed for these dogs to achieve their full size and mass potential), gender (the risk for males is 20 – 50% greater), and metallic implants to fix fractures.

• Chronic trauma and microscopic fractures have been proposed as risk factors, but this is difficult to prove conclusively. 

Spaying or Castrating

There was a study from David Waters group (Cooley et al., 2002), where survey data provided by owners showed an increase in risk to develop osteosarcoma in dogs that were spayed or castrated at an early age.

• The relative risk estimated from this study was as high as 4-fold higher for dogs neutered before one year of age than for intact dogs.
• Glickman’s group published similar data in 1998 based on analysis of cases in the Veterinary Medical Database (Ru et al., 1998). These studies generated significant debate and concern among veterinarians and owners. Nevertheless, the results have not been reproduced consistently in other large population studies (for example, Phillips et al and Scottish Deerhounds).

While these results may have increased some owners’ reluctance to neuter or spay dogs, the possible 3-fold increase in risk of osteosarcoma in females should be placed in context of the 80 – 260-fold reduced risk of mammary cancer by early spaying. (AKC Canine Health Foundation)