Cancer of the Bones of the Legs

The purpose of this handout is to discuss the diagnosis, prognosis and treatment of possible neoplastic (cancer) lesions in the leg bones of dogs.

Dogs with these type lesions present with lameness. Radiographs (X-rays) localize the lesion and rule out soft tissue problems.

Cancer must be our number one possible diagnosis in older dogs. Osteosarcoma is the most common bone cancer in dogs (85%). Osteosarcoma is a very metastatic and malignant tumor. By this, we mean that it spreads, usually to the lungs and this is the part of the disease that proves fatal.

Other possible cancers which could be present include chondrosarcoma, fibrosarcoma, hemangiosarcoma and other round cell tumors. Non-cancerous diseases are also possible and include osteomyelitis(bone infection) and mycotic (fungal) diseases and panosteitis. The most common fungal disease in this part of the country is coccidiodomycosis or Valley Fever. These non-cancerous diseases are more common in younger dogs. Panosteitis is a self limiting disease in young dogs, especially the German Shepherd.

Diagnosis of this lesion can be achieved via a bone biopsy. This is done with a special needle. Biopsies of this type are 92 % accurate at differentiating between cancer and non-cancer and are 82% accurate at differentiating between different types of cancer. In addition to biopsy, blood tests which check for antibodies and look at white blood cells are used to help diagnose osteomyelitis and Valley Fever.

If osteosarcoma is diagnosed, amputation of the affected limb is the treatment (a procedure called limb sparing ostectomy is available at some veterinary teaching hospitals). If there is no evidence of metastasis, combining amputation with chemotherapy improves survival. Of dogs which have amputation and chemotherapy, approximately 40% survive for one year and approximately 20% survive for two years. If there is disease in the lungs or other internal organs, chances for long term survival decrease dramatically.

Other cancers are also metastatic and locally invasive. Treatment is amputation of the affected limb combined with chemotherapy. Average survival times vary with the type of cancer. Mycotic disease and osteomyelitis are treated for a long term with anti-fungal and antibiotic drugs.