Osteosarcoma is a cancer (malignant tumour) affecting the bones.
Bones in the limbs or the spine and skull can be affected, and where the limbs are involved the cancer often leads to weakening of the bone which may result in it becoming fractured (broken), with severe pain and lameness.
Even without a fracture developing, most cases of osteosarcoma will produce progressive marked pain and lameness.
Osteosarcomas can spread (metastasise) to local lymph nodes and to the lungs, but this does not necessarily occur. In the absence of metastases, surgery (where possible) may be curative although this may involve, for example, amputation of an affected limb.
Radiation and drug therapy may also be of value in some cases, usually as an adjunct to surgical management.