Lameness is a general term used to describe pain or discomfort experienced when your dog moves normally or exercises minimally. Although your dog may develop lameness due to arthritis, ligament or tendon tears, or cartilage injury, lameness is also a cardinal sign of osteosarcoma. Therefore, any unexplained or chronic lameness in your pet warrants further investigation. Chondrosarcoma (cancer that arises from cartilage)
Some tumors arise from tissues associated with bone and can mimic osteosarcoma. These include:
Fibrosarcoma (cancer that arises from fibrous connective tissues)
Synovial cell sarcoma (cancer that arises from the cells that line the joints)
Hemangiosarcoma (cancer that arises from the blood vessels)
These tumors are far less common than osteosarcoma and tend to affect the axial skeleton (skull, ribs and spine) more often than osteosarcoma.
Other causes of lameness that must be considered and potentially differentiated from bone tumors include:
Pathologic fractures. If your pet experiences a fracture with minimal trauma, a pathologic fracture should be considered. Although fractures are most often a result of trauma, they can also occur in bones that have been weakened by cancer. Evaluating an X-ray may lead to the suspicion that the bone is abnormal; however, definite diagnosis of a tumor requires a biopsy. Pathologic fractures will not heal if fixed using standard techniques.
Osteomyelitis (infection in the bone). This is an uncommon condition that occurs as a result of infectious organisms such as bacteria or fungi getting into a bone. These organisms most commonly gain entrance to the bone through an open wound, open fracture or rarely through the blood. The appearance of osteomyelitis may be similar to some bone cancers because it often appears as a proliferative or fuzzy mass-like lesion on an X-ray. Differentiating these types of infection from bone cancer typically requires that a biopsy and a culture be performed.
Bone infarction. Bone infarction is a very rare condition in which a blood clot blocks the blood supply to a bone, resulting in death of the bone. This appears as a lytic lesion (loss of bone) on an X-ray, which is similar to the appearance that bone cancer can have.
Metastasis of tumors to the bone. Very rarely a bone cancer can be due to the metastasis (spread) of cancer from a primary cancer elsewhere in your dog. The most common types of cancer that metastasize to bone are mammary gland cancer, multiple myeloma and lymphosarcoma. These types of cancers tend to have a distinctively different appearance on X-rays than osteosarcomas. Although their radiographic appearance may alert your veterinarian to their presence, a biopsy is still required to make a definitive diagnosis. It is important to distinguish tumors that have spread from other tissues to bone from those that arise in bone initially, because the treatment differs. For metastatic tumors, an attempt will be made to find out where the primary (initial site where the tumor arose) cancer is located. If your dog is diagnosed with cancer, your veterinarian may wish to consult with an oncologist (cancer specialist) to fully understand the specific behavior and treatment of the cancer.