Bone Cancer (Osteosarcoma) In Dogs

Osteosarcoma is the most common bone tumor in dogs and occurs primarily in dogs of large breeds and so-called giant breeds. Canine osteosarcoma is a very malignant and painful tumor with a high rate of metastasis.

Occurrence And Causes

Osteosarcoma most commonly occurs in large dogs near the joints on the front legs “away from the elbow” and on the hind legs “near the knee joint” (appendicular osteosarcoma). Osteosarcomas are less common in small dog breeds and are more likely to be found on the flat and short bones of the axial skeleton, for example on the jaw, skull, or ribs.

In addition to a genetic predisposition, traumatic triggers such as bone infarcts, bone fractures, and implants are also known to cause osteosarcomas.

Breeds that are particularly frequently affected are Rottweilers, Irish wolfhounds, greyhounds, mastiffs, St. Bernards, and German shepherds.

Symptoms/Biological Behavior

Patients with osteosarcoma of the limb showed marked lameness in the affected leg. The lameness is caused by severe pain caused by the growth of the tumor. Later, swelling of the affected region occurs. In advanced cases, the leg can break (pathological fracture). Osteosarcomas in dogs almost always metastasize to the lungs via the bloodstream. Metastasis to other organs such as bones, liver, or skin is less common.

Diagnosis

The most important examination when suspecting osteosarcoma is the X-ray. Based on typical changes in the X-ray image, such as dissolution of the bone (cortical lysis), bone growth (osteoproliferation), and elevation of the periosteum (period), the suspected diagnosis of osteosarcoma can often already be made. It is also typical that the tumor occurs in the area of ​​the growth zone (metaphysis) and does not extend beyond the joint. Tissue removal (biopsy) can confirm the diagnosis and possibly determine the tumor grade in more detail. Unfortunately, taking a biopsy is often difficult and in some cases without clear histological findings. With computed tomography (CT), the spread of the tumor and the destruction of the bone can be shown more precisely and biopsy removal can be facilitated. The aggressiveness of the tumor can be determined more precisely by determining the enzyme alkaline phosphatase (AP). Dogs with a high AP have a poorer prognosis than patients with a low AP.

Therapy

Surgical removal of the tumor is the most important therapeutic measure. Limb tumors usually require amputation of the leg. Limb-sparing operations (limb-sparing) are only possible in a few cases in dogs and are offered by some specialists. While the pain and the local spread of the tumor are controlled with the operation, concomitant chemotherapy is necessary to prevent the growth of metastases. If an operation is not possible, the focus is on pain therapy. In addition to the combination of different painkillers and the use of bisphosphonates, irradiation of the affected bone (radiotherapy) is an important therapeutic option for reducing pain. New supportive immunotherapies for the treatment of osteosarcoma are under development

Prognosis

Although osteosarcoma in dogs has not yet been cured, a combined (multimodal) therapy consisting of surgery, chemotherapy, and pain therapy can extend the patient’s survival time and improve their quality of life.