What is Osteosarcoma?
Osteosarcoma (OSA) is the most common bone tumor in dogs and can sometimes present in cats. It usually occurs in the leg bones of larger breeds.
Osteosarcoma most often arises in middle-aged or elderly dogs but can arise in a dog of any age with larger breeds tending to develop tumors at younger ages. This aggressive type of cancer can develop in any bone, but the legs account for 75 – 85% of affected bones.
Osteosarcoma develops deep within the bone and becomes more painful as it grows outward destroying bone as it progresses. The lameness goes from intermittent to constant over 103 months. Obvious swelling becomes evident as the tumor grows and normal bone is replaced with cancerous bone.
Cancerous bone is not as strong as normal bone and can break with a minor injury. This type of broken bone is called a “pathologic fracture” and may be the finding that strongly suggests the presence of bone cancer. Pathologic fracture will not heal.
Osteosarcoma is often diagnosed via radiographs (x- rays) as it usually has a distinctive pattern, but a definitive diagnosis is made by bone biopsy. CT scans and MRIs are also helpful.
What Symptoms Can Present as the Disease Progresses?
- Swelling or mass at the site of cancer
- Lameness and/or limb pain
- Change in appetite
- Weight loss
- Licking the affected area
- Tender to the touch
- Exercise intolerance
- Persistent early stages
- Non-weight bearing lameness
- Vomiting and or/diarrhea
- Affected limb swelling/edema
- Ruptured skin over the site/infection
- Pathologic fracture
- Difficulty breathing/coughing
- Unable to stand
- Paralysis if spine involved
Crisis – Immediate veterinary assistance needed regardless of disease:
- Difficulty breathing
- Prolonged seizures
- Uncontrollable vomiting/diarrhea
- Sudden collapse
- Profuse bleeding – internal or external
- Crying/whining from pain*
*It should be noted that most animals will instinctually hide their pain. Vocalization of any sort that is out of the ordinary for your pet may indicate that their pain and anxiety have become too much for them to bear. If your pet vocalizes due to pain or anxiety, please consult with your tending veterinarian immediately.
Common Signs of Pain
Panting, lameness, difficulty sleeping, pacing, abnormal posture, body tensing, poor grooming habits, tucked tail, dilated pupils, licking sore spot, muscle atrophy, decreased appetite, vocalizing/yowling, reclusive behavior, aggressive behavior, avoiding stairs/jumping, depressed, unable to stand.
How Is OSA Treated?
Treatment of OSA has one or two goals: to try to cure cancer or simply manage pain and symptoms if a cure is not possible. Managing pain and trying to slow the progression includes the use of pain medicine, radiation therapy, limb amputation, and chemotherapy.
Curative intent options include combining different modes of therapy such as surgery, radiation therapy, and chemotherapy. However no matter the combination used, many dogs with OSA ultimately die due to the high metastatic potential of this tumor. Cats tend to do great with surgery alone.
What Is the Prognosis for OSA?
Unfortunately, by the time the disease reveals itself, it has more than likely already metastasized (spread) to other areas of the body such as the lungs, other bones, lymph nodes, and internal organs. If the cancer has already spread to the lungs upon diagnosis, chemotherapy may not be as effective and may only add a couple of months to the pet’s life.
If treatment is started before clinically detectable metastasis, it is possible to extend life by a year or more. Signs are dependent on the severity of the disease and whether or not treatment options are elected.
A personalized treatment plan is important to slow the progression of OSA. Talk to your veterinarian regarding the best treatment protocol for your pet.